Summary of Knowing the Love of Christ: An Introduction to the Theology of St. Thomas Aquinas by Michael Dauphinais & Matthew Levering

This is my summary of this great introductory book to St. Thomas Aquinas’ theology. My goal in this summary is merely to provide some basic ideas and inspire you to read this book and go deeper in your own theological reflection.

Introduction

Dauphinais and Levering present theology as a mountain ascent, with union with God as the summit. As novice climbers, we need a reliable guidebook—Aquinas’ Summa Theologiae.

For Aquinas, theology studies God and all things in relation to Him, from creation to ultimate fulfillment (ST I, q.1, a.7). The Summa reflects this journey, beginning with the Trinity as our origin and culminating in eternal communion with God. Each question is like a step toward this summit. This book follows Aquinas’ path, structuring its eight chapters after the Summa, guiding readers toward their own ascent to God.

Chapter 1: The Triune God

Since God is the beginning and end of all things, Aquinas begins his ascent up the spiritual mountain with a study of God. For simplicity sake, I will explain how God is one through the Old Testament revelation to Moses and how God is three through the New Testament revelation of Jesus Christ.

God as One: The Old Testament

Aquinas begins his study of God by looking at God’s revelation to Moses out of the burning bush as “I AM WHO I AM” (Ex 3:14–16). The burning bush is more than a miracle—it’s a profound symbol of God’s nature. This image reflects key aspects of God’s being that Aquinas explores: existence, simplicity, perfection, knowledge, will, and love. The following parallels with the burning bush are my additions, which I will expand in another article.

1. God’s Existence: Imagine standing before the burning bush as Moses did. The bush is aflame, yet untouched by the fire. This signifies that God exists in a way unlike anything else. Like fire, God is active, alive, and dynamic—but unlike fire, He doesn’t rely on “fuel” to sustain His existence. He simply is—the eternal source of all being.
2. God’s Simplicity: The single, unified flame symbolizes the far-greater reality that God is simply, undivided, pure Act—no potential waiting to be fulfilled, no division within Himself.
3. God’s Perfection: The undiminished fire symbolizes God’s perfection as the infinite fullness of being, without lack or deficiency. As Aquinas says, “A thing is perfect in proportion to its state of actuality” (ST I, q.4, a.1). Since God is infinite Act, He is perfect—nothing can be added to Him.
4. God’s Knowledge: The fire of the bush illuminates without being lit by anything else. Similarly, God’s knowledge is self-sufficient. He doesn’t learn or discover; He simply knows. His knowledge is identical to His being—eternal, simple, and complete.
5. God’s Will and Love: God’s will is like the fire—powerful, purposeful, and transformative. But unlike earthly fires that consume and destroy, God’s love is creative and life-giving. In loving Himself as the supreme good, God freely wills to share His goodness with creation (the warmth from the fire). As Aquinas says, “God’s love infuses and creates goodness” (ST I, q.20, a.2).
6. God’s Justice and Mercy: The command to remove sandals symbolizes justice (God’s holiness) and mercy (His desire to save His people). God’s justice gives all things their due, but His mercy exceeds justice, offering grace.

The burning bush teaches that God is both revealed and hidden—we know Him through His self-revelation, yet His essence remains beyond full comprehension. Like Moses, we are called to stand in awe before the unconsumed flame, drawn deeper into the mystery of divine love.

God as Three: The New Testament

Jesus Christ reveals Himself as the divine I AM, the very name given to Moses at the burning bush: “Before Abraham was, I AM” (Jn 8:58). His miracles—calming storms (Mt 14:27), walking on water, rising from the dead—confirm His divine identity. After His resurrection, He promises His disciples, “Behold, I am with you always” (Mt 28:20), and commissions them to baptize “in the name of the Father, and of the Son, and of the Holy Spirit” (Mt 28:19), explicitly revealing the mystery of the Trinity: one God in three divine Persons.

1. Eternal Processions: Within the Godhead, the Son proceeds from the Father as a word from the intellect—eternally begotten yet never separate: “In the beginning was the Word, and the Word was with God, and the Word was God” (Jn 1:1). The Holy Spirit proceeds from the Father and the Son as the love between them, uniting without dividing. These processions, being eternal and spiritual, neither multiply nor change God’s essence.
2. Temporal Missions: The missions of the Son and Spirit make manifest the eternal processions. The Incarnation reveals the Son’s procession from the Father, while the sending of the Holy Spirit at Pentecost manifests His procession from the Father and the Son. These missions draw creation into the divine life.
3. Analogy of the Mind: St. Thomas explains the Trinity using the structure of the human mind: The Intellect generates an inner word when it understands. The Will responds with love to what it knows. These processions are distinct yet do not divide divine unity.

The doctrine of the Trinity is an essential starting point, as it provides both the reason and blueprint of all of salvation history, as will be shown below.

Chapter 2: Creation, Providence, and Sin

Creation

For Aquinas, creation is not merely a past event but an ongoing act in which God continuously sustains all things in existence. Creatures depend entirely on God, while God alone is self-existent (ipsum esse subsistens). The Creator-creature distinction is absolute: creatures receive being, but God is being itself.

The New Testament reveals creation as the work of the Trinity: “All things were made through [the Word]” (Jn 1:3). The Father creates through His Word (Son) and Love (Spirit). The divine processions—wisdom (Son) and love (Spirit)—serve as the model for creation, which flows freely from God’s goodness.

Aquinas identifies three causes in creation:

1. Efficient Cause: God creates ex nihilo (from nothing).
2. Exemplar Cause: The world is ordered according to divine wisdom.
3. Final Cause: Every creature is directed toward its perfection in God.

Aquinas structures his Summa Theologiae around this dynamic:

1. Part I: God as Creator—exploring God’s nature and the act of creation.
2. Part II: The journey of rational creatures back to God through wisdom and love.
3. Part III: Christ as the way to union with God.

Thus, creation is a movement: all things come from God and return to Him, drawn by His wisdom, sustained by His love, and fulfilled in eternal communion.

Providence

Since creation is an ongoing act in which God sustains everything at every moment, Aquinas’ doctrine of providence explains God’s eternal plan to direct creation toward its purpose and His temporal execution of that plan, including both necessary and contingent events.

God governs the world not by eliminating created causes but by empowering them. As the Primary Cause who gives all things their being and directs them, God bestows upon creatures the “dignity of causality” as secondary causes to act within His providential designs. Thus, human actions are both entirely free and entirely under God’s providence. Since God is the creator, designer, and sustainer of our wills, He can move our wills without violating its freedom.

A special subset of providence is predestination, which explains God’s special governance over rational creatures leading them to eternal life, while reprobation explains God’s permission for some to reject Him and be eternally separated from Him.

Man as Created in the Image of God

Among created beings, humankind stands at the center of theological inquiry, because God took on a human nature in Jesus Christ. Humans stand at the nexus of the spiritual creation (angels) and the material creation (rocks, plants, dogs).

Genesis 1:27 states, “God created man in his own image.” But what does this mean? Unlike Christ, who alone is the perfect image of God (Col 1:15), humans are imperfect images, called to grow into greater likeness to God.

Aquinas teaches that this image primarily lies in our rational soul, which gives us the capacity to know and love God. The soul is the animating principle of the body, uniting intellect and will. Our highest calling is to imitate God by knowing and loving Him. Aquinas describes three levels in which humans reflect God’s image:

1. Nature: Every rational creature possesses the ability to know and love God, even if it does not do so in practice. Just as a mirror has the potential to reflect an image, every human is naturally capable of reflecting God.
2. Grace: The image of God is more fully realized when humans actively know and love Him. Grace acts as the “light of the soul” that enables the soul to recognize and reflect God’s presence more perfectly.
3. Glory: In heaven, the blessed achieve perfect knowledge and love of God. Here, the divine image reaches its fulfillment, as the saints see God as He is.

Sin

Humanity, created in God’s image and destined for glory, fell through original sin, described symbolically in Genesis 3. Adam and Eve’s choice to disobey God—seeking to “be like God” (Gen 3:5)—marked the first act of pride, prioritizing self over divine order. This sin fractured not only their relationship with God but wounded all of creation.

1. Original Sin: We were created with nature (reason & free will) and grace (divine life within), but original sin wounded human nature and destroyed grace. The intellect became darkened, the will weakened, and humanity subject to suffering, death, and disordered desires. Grace, the soul’s light for knowing and loving God, was lost. Like members of one body affected by the head’s choice, we all inherit the effects of original sin from Adam (see Rom 5:12-15).
2. Actual Sin: Mortal sin is a grave offense that destroys grace, rupturing one’s union with God (e.g., serious sins committed with full knowledge and deliberate consent). Venial sin is a lesser offense damage but do not sever one’s relationship with God.
3. Sin Within God’s Plan of Providence: God is not a failed creator. Although He knew humanity would fall, He also willed from eternity the remedy—the Incarnation of Christ. God’s providence encompasses both the Fall and Redemption. As the Church sings at Easter: “O happy fault, O necessary sin of Adam, that merited so great a Redeemer!” (Exultet). Sin reveals humanity’s need for grace, and God’s response in Christ surpasses the tragedy of the Fall. The cure is greater than the disease, transforming even our brokenness into an opportunity for divine mercy and redemption.

Chapter 3: Happiness and Virtue

Aquinas begins moral theology with the pursuit of true happiness—not fleeting pleasure but the highest good: union with God. Like climbers choosing the right path, humans must cultivate virtues to stay on course. Sin disrupts the journey, but grace sustains and guides us.

Moral Structure of Human Action: Every moral act has three essential elements:

1. Intention: The goal (desiring the summit).
2. Object: The action itself (taking the right steps).
3. Circumstances: External factors (weather, terrain).

For an action to be truly good, all three must align with virtue. No good intention can justify an evil act.

Training the Passions through Virtues: Passions influence our moral choices:

1. Concupiscible passions: Responses to the perceived good (e.g., love, desire, joy).
2. Irascible passions: Responses to difficulties and threats in attaining the good (e.g., anger, hope, fear).

Like a climber mastering endurance, virtue trains these passions to align with reason and moral excellence. Virtues are stable dispositions toward good, cultivated by practice and divine grace.

1. The Moral Virtues: (1) Prudence – Practical wisdom in choosing the right means – to chose the best route up the hill; (2) Justice – Giving others their due – treating fellow climbers fairly; (3) Courage (Fortitude) – Strength in facing difficulties – Persevering through the steepest inclines; (4) Temperance – Moderation of desires – Managing resources wisely and not overexerting oneself. –> These 4 moral virtues are further divided into acquired virtues, developed through effort and practice, and infused virtues, received from God through grace.
2. The Theological Virtues: These virtues are direct gifts from God & lead to intimate union with God: (1) Faith – Glasses – to see correctly – faith is supernatural knowledge of God; (2) Hope – A ticket to enter the summit – hope directs the soul to the summit, trusting in God’s power and mercy; (3) Charity – Food and drink – charity is friendship with God, transforming all virtues. It perfects faith (knowing God) and hope (trusting in Him) into love (delighting in Him for His own sake).

Virtues perfect the powers of the human soul, with moral virtues refining human nature and theological virtues elevating the supernatural life of grace. While distinct, nature and grace interpenetrate—grace does not replace nature but perfects it (gratia non tollit naturam, sed perficit).

7 Gifts of the Holy Spirit: Aquinas emphasizes the seven gifts of the Holy Spirit (Is 11:2–3) as dispositions that perfect the soul’s receptivity to divine guidance:

1. Wisdom – Seeing the summit clearly. Helps charity.
2. Understanding – Knowing the path. Helps faith.
3. Counsel – Making the right choices. Helps prudence.
4. Fortitude – Strength to endure hardships. Helps courage.
5. Knowledge – Recognizing the best course of action. Helps faith.
6. Piety – Deepening love for the journey’s purpose. Helps justice.
7. Fear of the Lord – Maintaining humility before the mountain’s grandeur. Helps temperance.

These gifts complement the virtues, ensuring that Christian moral life is not just about following rules but about living in friendship with God.

Freedom to Climb: Virtue and Freedom: Some might see rules and virtues as burdensome, limiting their freedom. But true freedom is not the ability to take any path—it is the ability to reach the summit. Just as a trained hiker can climb where an untrained one would stumble, a virtuous person is free for excellence—able to choose the good with ease. Modern society often values “freedom from” constraints, but Aquinas emphasizes “freedom for” excellence. Without training, no one is free to scale a mountain; without virtue, no one is free to live rightly. The commandments do not restrict human flourishing; they guide it toward happiness. The commandments are like fences that prevent us from falling off the cliff during our climb. The moral law and virtue work together in leading a person to ultimate fulfillment in God.

Conclusion: The Summit of Holiness: The goal of the climb is to reach the peak, to stand in awe of the breathtaking view. The Christian life leads to the ultimate summit—union with God. Aquinas teaches that virtue, perfected by grace, transforms a person into the image of Christ. This is why Jesus commands, “Be perfect, as your heavenly Father is perfect” (Mt 5:48). In heaven, the virtues find their fulfillment. Faith gives way to sight, hope to possession, and only charity remains, as eternal love in God. Until then, we climb. The path is steep, but the summit is worth the journey.

Chapter 4: Law and Grace

Humans are created for union with God, yet we lack the ability to reach this goal alone. Sin fractures our path, leaving us unable to ascend. God provides two essential aids: law and grace—our divine map and supernatural oxygen, guiding and sustaining us on the climb.

Mapping the Route: The Role of Law: Law is not a restriction but the path to true freedom, ensuring we reach our goal. Aquinas identifies five types of law:

1. Eternal Law – God’s master plan, governing creation.
2. Natural Law – The moral compass within us, though weakened by sin.
3. Human Law – Societal laws promoting order.
4. Divine Law – God’s revealed commands, marking the safest route.
5. Old & New Law – The Old Law (base camp) prepares for the New Law (final ascent).

Base Camp: The Old Law as Preparation

Before tackling the final ascent to the summit, climbers must acclimate at base camp, strengthening their endurance and conditioning their bodies for higher altitudes. The Old Law, given to Israel through Moses, serves a similar purpose. It prepares the soul for higher things but does not yet provide the full power needed to reach the peak.

The Old Law had three key functions:

1. Moral Law (e.g., the Ten Commandments) – Like essential survival skills, ensuring that climbers can navigate safely.
2. Ceremonial Law (e.g., temple sacrifices) – Like training exercises, ingraining discipline and pointing ahead to Christ.
3. Judicial Law (e.g., societal rules for Israel) – Like camp regulations, fostering order in preparation for the greater journey.

While the Old Law showed the path, it could not give the strength to climb. The Israelites continually failed, revealing the limits of human effort alone. The summit remained distant. Climbers needed more than instructions; they needed power.

The Final Ascent: The New Law of Grace: An inexperienced climber cannot summit a mountain on willpower alone. At extreme altitudes, oxygen thins, and even the strongest climbers falter. Without supplemental oxygen, reaching the peak is impossible. Grace is our supernatural oxygen—it elevates us beyond our natural abilities, allowing us to reach heights otherwise unattainable.

The New Law of Christ is not merely an updated set of instructions. It is the very life of God within us. The Old Law ordered the climber toward the summit; the New Law carries the climber upward.

• Christ fulfills the Old Law: The commandments are no longer external rules but are now written on our hearts (Jer 31:33).
• Jesus and Holy Spirit are our teachers and guides: Grace is not just a helping hand; it is God Himself lifting us higher. Invisible missions. The New Law signifies (1) the grace of the Holy Spirit, leading us to our supernatural end; (2) the tangible gift of the sacraments – which communicate grace to us, and the New Testament, which instructs us how to use well his grace (“climber’s manual”). The New Testament reveals that the whole of the moral life is ultimately the imitation of Christ. “Christ is the first and principal teacher (doctor) of spiritual teaching (doctrina) and faith” (II-II, q.7, a.7). Christ is the teacher par excellence, who in teaching the new law of grace not only guides us and forms us, but even re-creates us in his image. They are the best teachers because they not only communicate information, but also model a way of life, and give a power to do it!

Supernatural Climbing Gear: Grace in Action

Grace is not a crutch—it is the supernatural support that enables the climber to reach heights otherwise impossible. This distinction allows us to see how grace, which transforms the essence of the soul (the image of God), is the foundation for all of the Christian virtues that perfect the powers of the soul. St. Thomas explains grace in several ways, 3 main categories:

1. Habitual Grace – Like an unlimited oxygen supply, sustaining us for the journey (this is the “state of grace” received in Baptism, is lost only through mortal sin, and weakened in venial). VS. Actual Grace – Like a sudden burst of energy, immediate help for specific moments (given in moments of trial or temptation). Actual grace increases through prayer, devout reception of the sacraments, and the spiritual and corporal works of mercy.
2. Operative Grace – God’s initial pull toward conversion, like receiving a free ticket for the climb: The effect? Initial justification of the sinner (total gift). The person moves from being a child of Adam to being a child of God. VS. Cooperative Grace – Our response, as we climb with God’s help. The effect? Human merit. As children of Adam, we can merit nothing before God; as God’s own children, “partakers in the divine nature,” we can.
3. Sanctifying Grace – The core strength that makes us fit for heaven- grace that makes the recipient holy. VS. Gratuitous Grace – Special gifts like prophecy or healing, used to help others along the trail, to make others holy.

Without grace, we remain stuck in the valleys of sin, never progressing beyond the base of the mountain.

Freedom on the Trail: Law and Grace Together

Some might think that following rules and relying on grace restricts freedom, but this is like saying that trail markers restrict a climber’s ability to roam freely. True freedom is not wandering aimlessly—it is the ability to reach the summit. Modern views of freedom often focus on the freedom from external constraints (like a climber refusing to follow a trail), but true freedom for excellence is the ability to reach the goal without falling. Divine law is not a burden; it is the safest and most direct path to fulfillment. Christians are not merely rule-followers; they are climbers equipped with supernatural strength, led by the divine guide, moving toward the peak of holiness.

Conclusion: The Summit Awaits

At the end of the journey, the summit opens before us—a breathtaking view, the fulfillment of all desire. The ultimate goal is not just to avoid falling but to reach the heights of divine life. The New Law of grace, far from being a burden, lifts us beyond what we could ever achieve alone. The Beatitudes, the gifts of the Spirit, and the indwelling of divine life propel us toward our final destiny. As we continue our ascent, let us remember: “I press on toward the goal for the prize of the upward call of God in Christ Jesus.” (Phil 3:14). The climb is arduous, but the summit—eternal life with God—is worth every step.

Chapter 5: Jesus Christ

Our Guide to the Summit

Jesus declares, “I am the way, and the truth, and the life” (Jn 14:6), revealing that He is the ultimate path to human fulfillment—union with God. Like a seasoned mountaineer guiding climbers through treacherous terrain, Christ not only shows the way but empowers us to reach the summit. His teachings are not mere instructions but a revelation of divine truth, equipping us with what we need to complete the ascent. St. Thomas affirms that “Christ as man is our way back to God” (ST I, q.2, prologue). Yet, understanding Christ’s dual nature as fully God and fully man remains a challenge, often misunderstood even by those who follow Him.

Our Guide Foretold: The Promised Messiah

Throughout the Old Testament, prophets foretold the coming of a shepherd-king who would lead God’s people to safety. The kings of Israel, anointed to represent God’s guidance, often failed in their role, leaving the people lost. God Himself then promised, “I myself will be the shepherd of my sheep” (Ezek 34:15–16). Jesus fulfills this promise, declaring, “I am the good shepherd” (Jn 10:11), signaling that He is both the long-awaited Messiah and God Himself: “I and the Father are one” (Jn 10:30). He is the ultimate guide, the only one capable of leading humanity safely to its final destination. As a human being, he could stand among human beings fulfilling the role of the Lord’s anointed to mediate God’s presence. Only God could shepherd us well; yet we could only see a human shepherd. Jesus Christ in his divine and human natures fulfills both needs.

Our Guide Today: The Church

After His ascension, Christ did not leave His followers without direction. He sent the Holy Spirit to guide the Church, His Mystical Body, ensuring that His leadership continues. He also appointed Peter and his successors as earthly shepherds, commissioning them: “Feed my sheep” (Jn 21:15–17). Just as a climbing expedition relies on expert guides, the Church remains the visible presence of Christ, leading souls up the steep path toward eternal life.

God for Us: Why Did God Become Man?

“For God so loved the world that he gave his only Son, that whoever believes in him should not perish but have eternal life” (Jn 3:16). The force of this statement lies in the fact that it declares what the Incarnation accomplishes for us, namely, eternal life. Life eternal is simply another way of describing the ultimate end of man, or happiness. Life eternal describes the perfect union of the saints with God in heaven. How then does the Incarnation lead us to this goal? Aquinas identifies 5 key ways in which the Incarnation saves us (away from evil and toward the good):

1. Strengthening Faith – Christ’s teachings reveal divine truth with clarity, like a detailed map showing the safest route. The Incarnation also heals the wound of our pride by showing us the humility of God and takes away our presumption that we can heal ourselves spiritually (we were dead in sin).
2. Deepening Hope – His mercy reassures us that God desires our salvation. It also shows the great dignity of human nature. If God has deigned to assume our nature, then we should avoid any evil deeds that would debase human nature.
3. Kindling Charity – Seeing God’s love in Christ’s sacrifice moves us to love Him in return.
4. Providing a Perfect Example – Christ’s life models how we should live. Christ teaches us by enabling us to become like him in holiness.
5. Uniting Us with God – Through Christ’s humanity, we are elevated to share in divine life. Finally, in order that the human race be freed from sin, Jesus Christ made satisfaction for our sins. God has not simply commanded that the disorder caused by sin be repaired; he has come as a man to repair it from within human history. The Incarnation culminates in the cross, which reconciles sinners to God: “the New Law fulfills the Old by justifying men through the power of Christ’s Passion” (1-2, q.107, a.2)

There is a harmony or a beauty to the way God saves us through the Incarnation. God all-powerful could have saved us however he wished, but the Incarnation appears as the best and surest way to heal and transform the image of God within us. The movement toward good denotes our becoming like God; the withdrawal from evil signifies that God frees us from sin and the devil and even from debt owed to God. Redemption has two aspects: liberation from sin and union with God. In short, the perfection of the Incarnation manifests itself in the way that it accomplishes both the negative and the positive elements of our salvation. We are turned from evil by repentance and the forgiveness of sins (Lk 24:47). We are led into eternal life by becoming children of God (Jn 1:12). These twin focal points—forgiveness of sins and divine filiation—form the center of the new life in Christ.

Christ as Example: The Perfect Guide

To reach the summit of holiness, we must follow a leader who not only knows the way but embodies the goal. Christ’s humanity allows us to relate to Him, while His divinity ensures that He is the surest guide. He leads by both teaching and example, just as a mentor demonstrates technique while instructing climbers. His words carry authority: “You call me Teacher and Lord; and you are right, for so I am” (Jn 13:13). St. Thomas affirms that “examples move more than words” (ST II-II, q.34, a.1), and Christ’s actions provide the ultimate model.

There are two levels to imitating Christ: (1) Moral Exemplarity – Imitating His actions, such as His humility, patience, and self-sacrifice; (2) Ontological Exemplarity – Not just doing what Christ did, but becoming like Him by sharing in His divine sonship.

Christ is more than a teacher—He transforms us, making us adopted children of God.

The Mystery of Jesus Christ: Fully God, Fully Man

Understanding who Christ is becomes essential for understanding our salvation. The Church, guided by divine revelation, teaches that Jesus is one Person with two natures: divine and human. He is fully God and fully man, united in the “hypostatic union.” Just as a climber cannot ascend both land and sky simultaneously, no created being could unite divinity and humanity—but Christ, as the Word of God, accomplishes this without contradiction.

The concept “nature” answers the question “What is it?” and the concept “person” answers the question “Who is it?” When the disciples saw Jesus and asked, “What is Jesus?” both answers would be correct, “That’s a man” and “That’s God.” When the disciples asked, “Who is Jesus?” the answer would be “That’s the Son of God, the Second Person of the Trinity.” In fact, when Jesus asked, “Who do you say that I am?” Simon Peter answered, “You are the Christ, the Son of the living God” (Mt 16:15–16).

Consider it this way. Try to imagine a sheep-man who was fully ovine and fully human. You cannot. The reason why the two natures are incompatible with each other is that they are both created natures. As created natures, they occupy the same field of action. In this way, they are in a competitive relationship—either a sheep or a man, but not both. Now consider the union of two natures, one divine and one human. Here, there is a noncompetitive relationship because the divine nature is the source of the human nature, just as it is the source of every other created nature. Our inability to comprehend the divine nature stems from its distinction from creation.

The Humanity of Christ: The Perfect Instrument

Christ’s humanity is not merely a vehicle for divine presence but the means by which we receive God’s grace. His human intellect and will, perfectly united to His divine nature, allow Him to teach divine truths with clarity. His knowledge is both natural (acquired through human experience) and supernatural (infused through divine wisdom).

1. In His mind – He fully understands God’s plan while experiencing human learning. He saw the summit at all times (had the beatific vision). Christ’s vision of God enabled his words and deeds to express the divine Wisdom for all creatures. Just as St. Teresa of Avila’s experience of moments of contemplative union shaped her words and deeds, so also, in a higher way, Christ’s experiential knowledge of his Father in beatific vision illumined and governed his mission.
2. In His will – He fully submits to the Father’s mission while feeling real human suffering, as seen in Gethsemane. In similar fashion, grace conformed Christ’s human will to his divine will.
3. In His actions – His miracles flow from His divine power but are performed through His human nature.

Christ does not merely reveal knowledge—He communicates divine life. By assuming our nature, He transforms it, making it possible for us to ascend to God.

The Summit Awaits: Following Christ to Glory

Just as a climber needs a trustworthy guide, we need Christ to lead us to eternal life. His Incarnation, teachings, sacrifice, and continued presence in the Church ensure that we do not climb alone. He is the way, the truth, and the life—not just showing the path but empowering us to reach the summit. Through faith, hope, charity, and divine grace, we ascend toward the eternal heights of union with God.

Chapter 6: Salvation

When the risen Jesus explains why his cross is the light of salvation, rather than an absurd death, he reminds his followers to search the Old Testament which prepared for him: “Then he said to them, ‘O foolish men, and slow of heart to believe all that the prophets have spoken! Was it not necessary that the Christ should suffer these things and enter into his glory?’ And beginning with Moses and all the prophets, he interpreted to them in all the scriptures the things concerning himself” (Lk 24:25–27). Imitating Christ, Aquinas allows his theology of salvation to be formulated in the context of biblical Israel’s Mosaic Law and Temple, both of which are fulfilled by Christ and his Mystical Body.

Christ’s Fulfillment of the Mosaic Law

Understanding the necessity of Christ’s Passion requires first recognizing the burden of injustice in the world. The fall of humanity severed its relationship with God, necessitating an act of supreme obedience to restore justice. Christ’s Passion fulfills the Mosaic Law in three ways:

1. Ceremonial Precepts – Christ the Priest: Since the ceremonial precepts of the Mosaic Law were primarily those precepts instituting the sacrificial system for worship, Christ’s self-sacrifice fulfills the sacrificial rites of Israel’s worship (Heb 10:11–12). Christ’s sacrifice is total (as prefigured by burnt offerings) and is, as an act of love, an act of praise and thanksgiving (as prefigured by peace offerings). As a sin offering, Christ’s sacrifice operates—accomplishes its purpose—according to the modes of redemption and satisfaction.
2. Moral Precepts – Christ as Prophet: As the perfect prophet, Christ teaches the new law of love through his cross. Christ’s perfect charity on the cross embodies the Ten Commandments, exemplifying the greatest love by laying down his life (Jn 15:13). Charity is the foundation of fulfilling the Mosaic Law (1-2, q.100, a.10, ad 3). Christ’s perfect knowledge of God allows him to love fully, meriting glory for himself and his followers. His Passion creates a mystical communion, where the faithful participate in his merits through grace. Through his example and teachings, Christ fulfills the role of the prophet who reveals the fullness of divine truth. Like the prophets of the Old Testament, who recognized love as the primary element of sacrifice and indeed of worship, St. Thomas does not separate Christ’s cross from Christ’s love. Christ’s charity is what enables his cross to reconcile us to God and to each other. By teaching the new law of grace on the cross, Christ shows himself to be the true prophet.
3. Judicial Precepts – Christ as King: Christ, as the true King, restores justice by suffering on behalf of humanity. Christ takes upon himself the suffering due to sinners, fulfilling Isaiah’s prophecy of the suffering servant (Isa 53:4–6). He redeems or pays the debt by restoring the order of justice between humankind and God. The order of justice is revealed as an order of God’s gracious love. The kings of Israel failed to establish lasting justice, but Christ does so through his self-sacrifice. His suffering is directed toward each person individually, making his redemptive act universal yet personal. Suffering is transformed into a means of union with Christ: believers share in his sufferings to be glorified with him (Col 1:24). As King, Christ establishes his kingdom through justice, suffering, and love, fulfilling Israel’s expectation of a just ruler. The task of the king in Israel was to establish justice among his people. Christ, the true king, establishes justice for all humankind by his suffering, as the one who bears or endures their suffering due for sin.

“By recognizing that Christ’s cross fulfills the three kinds of precepts of the Mosaic Law, St. Thomas develops a theology of salvation that profoundly balances Christ’s sacrifice, Christ’s charity, and Christ’s suffering for others. He also shows why God gave such a prominent place in ancient Israel to the roles of priest, prophet, and king. In fulfilling the ceremonial precepts, Jesus is supremely priest; in fulfilling the moral precepts, he is supremely prophet or lawgiver (giving the law of love); and in fulfilling the judicial precepts, he is supremely king, losing his own life to establish justice among his people. Sometimes we hear it said that Christ’s suffering and death were random violence. In God’s plan, far from being random, they were the fulfillment of all justice—the righteousness of God—that the people of the Old Testament had been awaiting” (97).

Christ’s Fulfillment of Israel’s Temple

Aquinas’ understanding of salvation does not stop with the cross. It is necessary to grasp the power of the cross, but we would never understand salvation from this alone. After all, Christ rises from the dead and ascends to heavenly glory! The other mysteries of Christ’s life take their bearings from the cross, but they also cause our salvation in their own ways. We can illumine this relationship by once again turning to the Old Testament. Christ’s cross fulfills all justice, and thereby fulfills the Mosaic Law and reconciles everything on earth and in Heaven (cf. Col 1:20). The other mysteries of Christ’s life—preeminently his Incarnation, transfiguration, resurrection, and ascension—indicate the ways that we are united with the life of the Trinity. These mysteries reveal how human beings become temples of the triune God. They reveal how Christ’s perfect worship on the cross fulfills Israel’s Temple.

Christ’s Passion is not only the fulfillment of the Law but also of the Temple. 1 Kings 8 is the key biblical passage for understanding Israel’s Temple. God infinitely transcends the Temple (8:27); yet, God has nonetheless chosen to place his “name” there (8:29). Christ fulfills this mystery by becoming the true Temple, where God’s presence dwells bodily. Believers, as members of his Mystical Body, become the new Temple of God (1 Cor 3:16). We are made into the true Temple, the Mystical Body of Christ, by sharing in God’s “name” or identity—by our graced sharing in “He who is,” the divine life of blessedness. This is the salvation that God, in Christ, is offering us—to rejoice inexhaustibly in the mysteries of God’s love and wisdom.

The Incarnation: Manifested in Mary

Mary plays an essential role in the fulfillment of the Temple. In the Incarnation, Mary reveals the full meaning of God’s “presence” in the Temple and of the Temple’s holiness. Her fiat at the Annunciation initiates “a certain spiritual wedlock between the Son of God and human nature” (3, q.30, a.1). As an event analogous to marriage—the marriage of God and human nature—the Incarnation required the consent of the betrothed, and so “the Virgin’s consent was besought in lieu of that of the entire human nature” (ibid.). Aquinas highlights Mary’s role in the Incarnation in order to show that the Incarnation is not simply a preparation for the cross, but the inauguration of the fulfilled Temple, the visible Mystical Body of Christ.

The Transfiguration

The Transfiguration prefigures the resurrection and glorification of believers. The transfiguration begins to reveal how human beings, united to Christ, will share eternally in the divine life. In Christ’s transfigured body, we see that God will transform us into persons who can rejoice spiritually and bodily in eternal life. The transfiguration shows members of Christ’s Mystical Body that their suffering leads to glory. St. Thomas teaches, “Our Lord, after foretelling His Passion to His disciples, had exhorted them to follow the path of His sufferings (Mt 16:21, 24). Now in order that anyone go straight along a road, he must have some knowledge of the end…. Above all is this necessary when hard and rough is the road, heavy the going, but delightful the end” (3, q.45, a.1). The transfiguration is about the “end”—the fulfilled Temple, the perfect presence of God.

Why did Christ choose “shining” (clarity) to manifest, in his body, the glory of the fulfilled Temple? Clarity is the spiritual glory (holiness) of the soul overflowing into the body. This miracle occurred when Christ’s face “shone like the sun.” We have all seen people who seem to glow with happiness or with love. The outward glow indicates an inward peace. Clarity then was a way to manifest the “end” of the fulfilled Temple, in which all will be united by perfect holiness and love. St. Thomas emphasizes this application to the Mystical Body by distinguishing between the resplendence of Christ’s face and his garments. He writes, “Just as the clarity which was in Christ’s body was a representation of His body’s future clarity, so the clarity which was in His garments signified the future clarity of the saints, which will be surpassed by that of Christ, just as the brightness of the snow is surpassed by that of the sun” (III, q.45, a.2, ad 3). Christ’s whole Mystical Body will shine, but the source of its shining will always be Christ himself.

The transfiguration reveals the coming fulfillment of Israel’s Temple in two other ways. First, Moses and Elijah, along with the three chief disciples, were chosen to appear with Christ. This reveals the unity of the divine law; salvation includes not only those after Christ, but also those before him, and for both Christ is the source of salvation. As St. Thomas notes, “men are brought to the glory of eternal beatitude by Christ,—not only those who lived after Him, but also those who preceded Him” (III, q.45, a.3).

Second, at the transfiguration, God the Father, speaking out of the “cloud” (symbolic of the Holy Spirit), says, “This is my beloved Son, with whom I am well pleased; listen to him” (Mt 17:5). A similar manifestation of the Trinity had occurred at Christ’s baptism. Baptism takes away sin and confers innocence; the transfiguration prefigures the “end” or goal of baptism, namely, the conferring of heavenly glory in the fulfilled Temple. The event of the transfiguration reveals that Christ is about to bring Israel’s Temple to its fulfillment in his Mystical Body.

The Resurrection and Ascension

Christ’s Passion removes the penalty of sin, but the resurrection restores human nature to divine glory.

The resurrection is the exemplar cause of salvation, showing that human nature is destined for glory. In distinguishing between the causality of Christ’s cross and of his resurrection as regards our salvation, St. Thomas notes that “Christ’s Passion wrought our salvation, properly speaking, by removing evils; but the Resurrection did so as the beginning and exemplar of all good things” (3, q.53, a.1, ad 3; cf. Rom 4:25). This is the distinction between efficient and exemplar causality that we saw earlier. The cross restores justice and fulfills the Mosaic Law; the resurrection manifests human glorification and fulfills Israel’s Temple. Christ’s resurrection is the exemplar cause of the future resurrection of all human beings. Had Christ not been resurrected, we would never have had the hope that our bodies would truly share in eternal glory. If Christ’s resurrection is good news for all human beings, however, why did he not show himself to everyone after his resurrection? Christ showed himself only to a few, who then spread the good news, because evangelization is the task of the Mystical Body on earth.

Christ’s ascension prepares the way for believers to follow him into heaven: After his resurrection Christ did not stay on earth, but ascended to his Father in heaven. St. Thomas holds that the ascension is the means by which Christ “prepared the way for our ascent into heaven…. For since He is our Head the members must follow whither the Head has gone” (3, q.57, a.6). Indeed, when he ascended to heaven, the souls of the holy men and women who had been waiting in the “hell of the just” for his cross to take away the debt of original sin, ascended with him. Ever since Christ’s resurrection and ascension, the Mystical Body, Israel’s fulfilled Temple, has been present in heaven. Now that Christ is in heaven with his saints, he intercedes for those who are still journeying toward him. Citing Ephesians 4:10, St. Thomas notes that Christ ascended so that “being established in His heavenly seat as God and Lord, He might send down gifts upon men” (3, q.57, a.6). These gifts are the subject of the next chapter.

Chapter 7: Church and Sacraments

The History of Salvation

The Church is woven into the history of salvation, which unfolds in four states: before the Law, under the Old Law, under the New Law, and in glory. While the Church is fully revealed after Christ, it has been present in all ages through faith. The Mystical Body of Christ, as a “spiritual” reality, extends beyond visible boundaries; many have implicitly belonged to it through faith in divine providence (Heb 11).

With the Incarnation and Pentecost, the Holy Spirit acts with new intensity, drawing people explicitly to Christ. The Church is now visible in history, led by the apostles and their successors, teaching and administering the sacraments. While grace is given to all, evangelization is necessary because Christ’s explicit revelation transforms human relationships and history. Through the sacraments, God imparts grace in a manner suited to human nature—through tangible, visible signs.

The Nature of the Church

The Church is the community of friendship with Christ, formed by the Holy Spirit. Christ, the Head, unites his Mystical Body, making the Church one in truth and love (Col 1:18–20). Aquinas suggests that “the Holy Spirit is likened to the heart, since He invisibly quickens and unifies the Church” (III, q.8, a.1, ad 3).

Under normal circumstances, we receive the grace of the Holy Spirit most profoundly through the sensible signs, or sacraments, that mediate to us the power of Christ’s cross. St. Paul connects the sacraments to the crucifixion: “Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death?” (Rom 6:3). Since baptism unites us with Christ’s death on the cross, it also leads us to share in his resurrection. The Holy Spirit forms Christ’s Mystical Body primarily through sacramental grace.

While the Church is unified, it contains diversity in both active and contemplative lives, charismatic graces, and different vocations. Aquinas writes that “even as in the order of natural things, perfection, which in God is simple and uniform, is not to be found in the created universe except in a multiform and manifold manner, so too, the fulness of grace, which is centered in Christ as head, flows forth to His members in various ways, for the perfecting of the body of the Church” (2-2, q.183, a.2). Although God calls all Christians to charity, it belongs to the perfection of the Church to have a rich diversity among her members, so that each member might serve the others in accord with Christ’s example. This mutual service is not an end in itself, but rather aims at the perfection, by grace, of the virtuous life in each member and of the entire Body.

The evangelical counsels of poverty, chastity, and obedience are meant to be shorter and faster paths up the mountain of holiness. Nonetheless, the standard of holiness is the same for all the baptized: “The perfection of the Christian life consists radically in charity” (II-II, q.184, a.1). Every human being is called to this perfection. The Second Vatican Council described this reality as the “universal call to holiness.”

Purpose of the Sacraments

Since we are embodied spirits who experience the world through our senses & depend upon sense experience for acquiring knowledge, Christ, as a good Teacher, instituted sacraments as sensible signs that actually cause the spiritual change that they signify, as seen in baptism (Jn 3:5), confession (Jn 20:23), and the Eucharist (Jn 6:53–57). They serve human nature by making spiritual realities perceptible.

Sacraments shape the Church, making it one, holy, catholic, and apostolic. They extend Christ’s Incarnation (making the invisible God manifest physically), ensuring the Mystical Body remains united to its Head, as grace is applied to every stage of life. Just as Christ’s humanity is the “instrument” through which his divinity works our salvation in the world, the sacraments are related to Christ’s humanity as the instruments by which he, our savior and teacher, shares with human beings the new life that he has won for us. St. Thomas affirms that the Church “is built on faith and the sacraments of faith” (3, q.64, a.2, ad 2). Whereas in heaven we will no longer need the sacraments or the visible Church, the visible Church and the sacraments both correspond to the concrete, historical character of this present life.

The Individual Sacraments

1. Baptism – Incorporates one into Christ’s death and resurrection, remitting sin and conferring divine filiation. It permanently marks the soul with Christ’s image and makes us Israel’s Temple fulfilled. Baptism of desire and invincible ignorance acknowledge God’s ability to act beyond visible sacraments (III, q.68, a.2).
2. Confirmation – Strengthens baptismal grace, equipping the faithful to proclaim the Gospel. Like the apostles at Pentecost, confirmed Christians receive the Holy Spirit to endure trials and bear witness to Christ.
3. Eucharist – The greatest sacrament, as it contains Christ substantially, unlike the others which communicate grace instrumentally. The Eucharist is both sacrifice and meal, making present Christ’s eternal offering (Heb 7:25, 27). It unites believers to Christ’s Mystical Body and sustains them in divine charity.
4. Penance – Restores friendship with God after sin. Since sin affects the Mystical Body, confession is necessary to reintegrate the sinner into communion with Christ. The priest acts in persona Christi, applying Christ’s mercy sacramentally.
5. Anointing of the Sick – Heals and strengthens the soul in preparation for eternal life. While sickness results from the fallen condition, this sacrament unites suffering to Christ’s cross.
6. Marriage – A covenantal sacrament reflecting Christ’s love for the Church (Eph 5:32). It is intrinsically ordered to the procreation and education of children. Marriage is indissoluble because it is a participation in divine fidelity.
7. Holy Orders – Confers the authority to teach, sanctify, and govern the Church. Bishops, as successors of the apostles, maintain unity in faith. The pope, as Peter’s successor, ensures doctrinal continuity. The validity of the sacraments does not depend on the personal holiness of the clergy but on Christ’s institution.

The Church’s Authority and Unity

The Church, though fundamentally an interior communion of the Holy Spirit, remains a visible institution with apostolic governance. The Holy Spirit guides its doctrinal development, ensuring the integrity of Christ’s teachings (Jn 16:13). The authority of the pope and bishops does not rest on their merits but on Christ’s gift. Even when individuals fail, the Church remains holy, as its sacraments and doctrines are Christ’s own.

Faithful submission to the Church’s teachings is a sign of freedom, not constraint. True freedom is found in receiving Christ’s truth and love, which the Church safeguards. The Mystical Body functions as a communion of divine charity, guiding believers toward their final participation in the life of the Trinity.

Chapter 8: Eternal Life

St. Thomas Aquinas approaches eternal life not as an escape from history but as the fulfillment of it, culminating in the liturgical consummation of all things, when every knee shall bow before God (Is 45:23; Rom 14:10). By examining the “hints” given in Scripture, Aquinas seeks to understand these hints. He understands eternal life not as a flight from history, but as the liturgical consummation of history.

Hell: The Rejection of Divine Love

Before discussing heaven, St. Thomas considers its opposite: hell. God calls all to union with Him, but some freely reject this call. Those who choose selfishness over divine love are permanently separated from the Mystical Body of Christ. Though they remain within God’s order through divine justice, they exclude themselves from His presence. The damned, judged by Christ and the saints, confirm the Psalmist’s words: “The wicked…are doomed to destruction forever” (Ps 92:7). Through this justice even the damned belong to the perfect consummation of all things.

Christ, wielding the sword of divine justice, judges in righteousness (Rev 19:11–16). His cross becomes both mercy for the repentant and judgment for those who reject it. The saints, sharing in divine love, judge with perfect justice, rejoicing in God’s righteousness (1 Cor 6:2). Though some struggle with the idea of eternal punishment, Aquinas explains that charity desires justice, and the saints, purified in love, will rejoice in justice being fulfilled.

Hell is not an arbitrary punishment but the natural consequence of rejecting God’s love. As St. Peter writes, God wills that all reach repentance (2 Pet 3:9). Yet, for those who refuse, divine presence becomes torment rather than joy. The damned experience God’s justice not as love but as wrath because their own rejection of Him distorts their perception of His goodness.

Heaven: The Consummation of Creation

Heaven is the final fulfillment of the Mystical Body of Christ. The Book of Revelation describes this consummation as a new heaven and a new earth, where God dwells with His people, wiping away every tear and ending suffering (Rev 21:1–4). Unlike the earthly Temple, where God’s presence was veiled, in heaven, the Trinity itself will be the Temple, fully revealing divine intimacy (Rev 21:22–23).

The new creation includes not just glorified human beings but the entire cosmos, transformed and renewed. The material world will not be discarded but perfected, as all creation was originally ordered toward divine glory (Rev 10:5–7). There will be no more corruption or decay—only eternal harmony. Heaven truly is the renewal and transformation of the whole cosmos.

The Resurrection of the Body

In heaven, the body will be transformed yet remain the same individual body, free from original sin’s effects. St. Paul describes the resurrected body as imperishable, glorious, and spiritual (1 Cor 15:42–44). Aquinas identifies 4 key qualities of the glorified body:

1. Impassibility (Incorruptibility): The body will be free from suffering, disorder, and decay. It will be ruled perfectly by the soul, ensuring harmony.
2. Subtlety (Harmony): The glorified body will move freely without resistance, allowing seamless participation in heavenly worship. “There will be no crowding in the divine liturgy of heaven, no matter how many resurrected human beings are present.”
3. Agility (Perfect Movement): The body will move effortlessly, reflecting the soul’s perfect harmony with God. The praise offered bodily by the blessed in heaven will not be laborious or burdensome, and so they will not tire out and need to rest.
4. Clarity (Radiance): The glorified body will shine with divine light, as Christ did in His Transfiguration (Mt 17:2).

These qualities ensure that the glorified body participates fully in eternal liturgical worship, radiating the soul’s perfect union with God. Each of these qualities removes impediments to the body’s truly participating in the glorified soul’s everlasting worship. Through the beatific vision, in which we see God face to face and know him as he is, the faculties that differentiate human beings from other animals—namely, the ability to know and love God, and all things in relation to God—are transformed, elevated, and perfected.

Purgatory: The Final Purification

Aquinas acknowledges purgatory as the final stage of preparation for heaven. Those who die in God’s grace but still need purification undergo this process to be perfected in love. Purgatory purifies the soul from lingering attachments to sin, ensuring it can fully participate in divine glory.

Heaven as the Fulfillment of the Mystical Body

Heaven is the completion of Christ’s work of reconciling all things. The saints, angels, and renewed cosmos will form a perfect harmony of worship, united in divine love. This eternal communion is described as the marriage feast of the Lamb, where Christ and His Bride, the Church, rejoice forever (Rev 19:6–8).

Aquinas presents heaven as the culmination of all divine promises—the state where justice, love, and beauty are perfected. In heaven, the saints will experience the fullness of divine life, forever united with the Trinity in a communion of infinite joy.

Conclusion

This book has traced the Christian journey from its origin in the Trinity to its fulfillment in eternal communion with God. Yet, this is not an endpoint but an invitation to deeper contemplation. St. Thomas’s Summa Theologiae teaches us how to ask the right questions about faith, echoing Christ’s words: “Ask, and it will be given you; seek, and you will find” (Mt 7:7).

We have explored the divine wisdom and love that shape human life, recognizing how God, despite sin, leads history toward fulfillment. The desire for happiness is fulfilled in Christ, whose sacrifice restores us and opens the way to grace. Through the Church’s teachings and sacraments, we are conformed to his love and drawn into the mystery of divine gift.

Finally, we have glimpsed the joy of heaven, where the saints rejoice in perfect communion with the Trinity. This journey is far from over—it calls us to keep seeking truth and anticipating the day when our Teacher will reveal all things. Until then, we follow in faith, echoing the final call of Scripture: “The Spirit and the Bride say, ‘Come’… let him who desires take the water of life without price” (Rev 22:17).