Foreword
The aim of this book is to situate the Eucharistic mystery within the divine economy of supernatural life, according to the sacramental doctrine of the Church. A devoted disciple of St. Thomas Aquinas, Dom Anscar Vonier (1875–1938) presents the Eucharist through the lens of the sacramental principle: “Our Catholic doctrines can afford to be simple because the greatest minds have conspired in the effort of bringing them down from heaven to the level of our daily life” (iii).
A Key to the Doctrine of the Eucharist by Dom Anscar Vonier, Westminster, 1925. Reprint: Assumption Press, 2013.
1: Faith
The Catholic doctrine of the Eucharist exemplifies the broader question: how do individual human beings enter into union with Christ, redemption incarnate? How does one move from acknowledging Christ as the Redeemer to claiming Him as my Redeemer?
“The power of Christ’s passion is linked up with us through faith and through the sacraments. This, however, in different ways: for the linking up which is by faith takes place through an act of the soul, whilst the linking up which is by the sacraments takes place through the use of external things” (1). Faith is a real psychological contact with Christ that turns the great redemption into my redemption. It is the beginning of the spiritual life and “the first grafting of man on Christ which underlies all other fruitfulness” (3).
The sacraments complete and make more efficacious this contact—more real and more infallible in its effect (6). They are essentially sacraments of faith; both faith and sacraments are divinely empowered to open man to Christ’s redemptive treasury.
2: Sacraments
Aquinas writes, “Sacraments are certain signs protesting that faith through which man is justified” (12). This is a complete definition in its broadest sense. Faith and the sacraments are inseparable, though faith may be called the older, vaster, and more universal reality. “The sacramental system is grafted on faith; it is essentially the executive of our faith; it is, shall we say, the reward of faith” (10).
Why do we need the sacraments?
Because of fallen human psychology:
- Man’s nature: a composite of spirit and sense.
- Man’s estate: enslaved to material things, in need of spiritual power within material signs.
- Man’s activity: so prone to distraction, finding in the sacraments a concrete exercise that leads to salvation.
“The sacramental life of the Church is truly a perfect understanding of man’s needs” (12).
3: The Power of Sacramental Signification
“O sacred Banquet, wherein Christ is received, the memory of his passion is kept, the mind is filled with grace, and there is given unto us a pledge of the coming glory” (17).
The Eucharist has a triple sacramental signification:
- Past – “commemorative”: the death of Christ on the cross.
- Present – “demonstrative”: supernatural transformation in Christ, the reality signified by the symbol.
- Future – “prophetic”: eternal glory with Christ.
“Every sacrament, then, announces something: it brings back the past, it is the voice of the present, it reveals the future” (17). “All the sacraments give us the blessed power of stepping outside the present” (18).
To say a sacrament is merely “an external sign of an internal grace” is too narrow unless one includes both the cause of grace (Christ’s Passion) and its goal (eternal life). “A sign is that which, besides the impression it makes on the senses, puts one in mind of something else” (ST III, q.60, a.4, ad 1).
4: The Perfection of Sacramental Signification
“The sacraments of the new law are at the same time causes and signs” (21). They are the most perfect signs because they effect what they signify. A sacrament is a true carrier of its spiritual reality (48).
5: Sacramental Thought
The sacraments constitute a new world created by God, governed by unique laws (29). It is a “middle world” between creature and Creator—neither purely natural nor divine, yet partaking of both (33).
This world is marked by:
- The creative power of symbols
- The efficacy of signs
- The resourcefulness of simple things in God’s hands
Sacraments have their own mode of existence, psychology, and grace (30). They are not veils but complete realities in themselves.
6: The Sacramental Role
The sacraments serve a dual role:
- For man: sanctification
- For God: worship
Man participates actively by offering back to God His own gift. Thus, the sacrament is a res sacra, a sacred thing given for approaching God (40).
7: The Sacramental Setting of the Eucharist
“The Eucharist is the perfect sacrament of the Lord’s passion inasmuch as it contains the very Christ himself who suffered” (ST III, q.73, a.5, ad 2). The Eucharistic sacrifice is quintessentially sacramental.
The term “sacrament” covers the whole Eucharist as with a golden baldachino; the sacrifice of the Mass is sacrament in its fullest form. “The sacrifice of the Mass, if it has any human explanation, must be explained in sacramental concepts” (46–7). The purpose of the book is to make clear that in every aspect, the Eucharist is a sacrament (47).
8: Sacramental Harmony
The sacramental system is a single, unified organism in which all seven sacraments work in concert (53). The Eucharist reigns supreme:
- Christ is present substantially.
- All other sacraments prepare for and culminate in it.
- The Church’s sacramental practice centers on it.
It is “the Queen among the seven sisters,” not a solitary colossus but surrounded harmoniously by the others (54). The doctrine of supernatural instrumentality—divine tools in Christ’s hands—gives profound unity.
“A sacrament is that which contains something sacred… the Eucharist contains something sacred absolutely, I mean Christ himself” (ST III, q.73, a.1, ad 3). The consecration is the complete Eucharist because it is the complete memory of Christ’s Passion (58).
9–11: The Eucharist as Sacrifice
“The perfection of the sacrament is not in the use made of it by the faithful, but in the consecration of the matter; for the representation of Christ’s passion is performed in the very consecration of the sacrament” (ST III, q.80, a.7, ad 2–3). To offer the Mass is to make the sacrament; the celebration itself is a sacramental act.
The sacrifice of the Mass belongs to a sacramental order beyond human experience—it is a “sacrament-sacrifice” (71). “The sacramental sphere is an unknown world with a well-known inhabitant” (73).
How is the sacrament a sacrifice? Because it signifies a sacrifice—and what it signifies, it effects. “Sacramental signification is the only door through which we approach the nature of Christ’s sacrifice on the altar” (83). “The sacrifice is nothing else than the inward kernel of the external, symbolical rite of sacrifice” (84).
12–14: Eucharistic Representation, Application, Immolation
The Eucharistic Body and Blood, sacramentally separated, represent the historical separation on Calvary. This representation is not passive; it applies the redemptive power of the Cross to the soul.
“Christ is immolated in the Eucharistic sacrifice because the Calvary immolation is represented so truly and is applied so directly” (100). In the sacrament, we receive not the mortal or glorious Christ, but Christ directly after death, without visible wounds.
“The Eucharist is the sacrament of the passion of Christ, inasmuch as man is rendered perfect by being linked up with the dead Christ” (ST III, q.73, a.3, ad 3).
15–16: The Oneness of the Christian Sacrifice
The sacrifice of the altar and the sacrifice of Calvary are one and the same. Since the Eucharist is sacramental, it adds nothing new but perfectly represents the original.
“The priest and the victim are the same in sacramental sameness, as on Calvary they were the same in natural sameness” (120). The priest represents Christ as truly as the elements represent His Body and Blood. The sacramental priesthood and the sacramental sacrifice are intrinsically united (121).
The Mass is not a shadow of Calvary—it is a real sacramental act of equal perfection, a full offering in time (123). The Last Supper was likewise a full act, anticipating Good Friday (124).
17: Transubstantiation
The change of substance—Transubstantiation—is the divinely revealed key to sacramental truth. It is not the sacrament itself, but the hidden power that makes it real.
“Transubstantiation is at the root of the sacrament, deep down in the abyss of being, where God’s omnipotence is supreme” (141). It is the metaphysical condition for Eucharistic grace, just as the soul’s creation underlies human personality.
18–19: Eucharistic Difficulties and Concomitance
Christ’s Body and Blood are present literally but in a different mode of being than on earth or in heaven (157–8). This duality is central to the mystery.
Concomitance explains how the whole Christ is present under each species. The Body and Blood are not isolated—they are “escorted by friends” (161). The Eucharistic elements are surrounded by Christ’s soul and divinity.
20: Man’s Share in the Eucharistic Sacrifice
The Eucharist is a gift not only of Christ but of His sacrifice, offered to the Church and each Christian. “In the new law the true sacrifice of Christ is communicated to the faithful under the appearance of bread and wine” (ST III, q.22, a.6, ad 2).
This is not merely the application of grace—it is real participation in the sacrificial act. “A sacramental priesthood offers up a sacramental sacrifice” (178). The priesthood is the continuation of the Last Supper; the victim is the representation of Calvary (181).
Each Mass is a historical event with a measurable sacrificial worth. Two Masses are worth double the grace of one (180).
21: The Eucharistic Liturgy
The Church’s liturgy confirms the book’s thesis: the Eucharist is primarily seen as a sacrament. Because it is truly hers, the Church surrounds it with solemnity and symbolic richness.
Sacraments are the Church’s possession; thus, she expresses their divine reality through human artistry and devotion. This creativity is possible only because the Eucharist is a sacramental function, divine in substance, human in expression (188).
22: The Eucharistic Banquet
The sacrament-sacrifice is followed by sacrament-food (196). The Eucharist fosters charity, drawing members into mystical communion. Eucharistic grace is membership in Christ’s Body (199).
“The world’s salvation is in the Eucharist… not a hyperbolical phrase, but a sober statement of spiritual reality” (200).
23: Eucharistic Consummation
The sacraments are true prophecies of eternal life (203). “He who eats my flesh and drinks my blood has eternal life” (John 6:55).
There will be no Eucharistic sacrifice in heaven; instead, the Lamb’s sacrifice gives way to His nuptials with the Church (205). Earth is the place of sacrifice; heaven is its fulfillment.
Final Review
Dom Anscar Vonier’s A Key to the Doctrine of the Eucharist is a theological classic of rare clarity and depth. Drawing deeply from Aquinas, Vonier presents Eucharistic doctrine in a way that is logical, luminous, and pastorally rich. The sacramental structure of the book mirrors the sacramental mystery it unfolds: layered, coherent, and radiant with grace.
He succeeds in making Aquinas accessible without oversimplifying, unfolding each doctrine with measured clarity and integrating it seamlessly into the broader mystery of redemption. Vonier’s prose is dignified yet direct, his theological structure precise yet contemplative. This book is one of the most faithful and profound modern expositions of Thomistic Eucharistic theology—a true key to the mystery.
Prodigal Catholic 
Thank you This is very helpful and appreciate the time you took to do this. what a mystery of grace!
Just finished this book and this was just the help I was looking for in understanding the book. Thank you so much.