Summary of Mere Christianity by C.S. Lewis

Basic Summary

Based on a series of radio broadcasts during the Second World War between 1942 and 1944, Mere Christianity is Lewis’ explanation for the logical validity of Christianity. As a Christian apologetic, Lewis defends the basic Christian faith from its critics and also presents the basics of the Christian life.


For Lewis, Mere Christianity “is more like a hall out of which doors open into several rooms. If I can bring anyone into that hall I shall have done what I attempted. But it is in the rooms, not in the hall, that there are fires and chairs and meals. The hall is a place to wait in, a place from which to try the various doors, not a place to live in. For that purpose the worst of the rooms (whichever that may be) is, I think, preferable. It is true that some people may find they have to wait in the hall for a considerable time, while others feel certain almost at once which door they must knock at. I do not know why there is this difference, but I am sure God keeps no one waiting unless He sees that it is good for him to wait. When you do get into your room you will find that the long wait has done you some kind of good which you would not have had otherwise. But you must regard it as waiting, not as camping. You must keep on praying for light: and, of course, even in the hall, you must begin trying to obey the rules which are common to the whole house. And above all you must be asking which door is the true one; not which pleases you best by its paint and paneling. In plain language, the question should never be: “Do I like that kind of service?” but “Are these doctrines true: Is holiness here? Does my conscience move me towards this? Is my reluctance to knock at this door due to my pride, or my mere taste, or my personal dislike of this particular doorkeeper?” When you have reached your own room, be kind to those who have chosen different doors and to those who are still in the hall. If they are wrong they need your prayers all the more; and if they are your enemies, then you are under orders to pray for them. That is one of the rules common to the whole house” (10-11).

Book 1: Right and Wrong as a Clue to the Meaning of the Universe

In the first part of the book, Lewis discusses the “law of human nature.” When studying human history, he claims, one is struck by how similar different societies’ moral codes are, at least at a fundamental level. Lewis argues that moral law isn’t just an arbitrary human invention—it’s actually a real, timeless thing—invented by an all-powerful being who stands outside the confines of material space and time, and reveals itself to humans through moral law.

“These, then, are the two points I wanted to make. First, that human beings, all over the earth, have this curious idea that they ought to behave in a certain way, and cannot really get rid of it. Secondly, that they do not in fact behave in that way. They know the Law of Nature; they break it. These two facts are the foundation of all clear thinking about ourselves and the universe we live in” (18).

Book 2: What Christians Believe

In the second part of the book, Lewis discusses a few competing theories about the all-powerful being’s identity.

Some religious groups, the Pantheists, believe that the all-powerful being, God, is neither good nor evil. Pantheists believe that God is the universe, meaning that everything in the material universe is divine.

Other religious groups, such as Muslims, Jews, and Christians, believe that God created the universe, yet is distinct from it; thus, God is good, and wants humans to work hard to make the universe a better place.

Christians also believe in the existence of an ultimate evil, the Devil. However, in Christianity, evil isn’t equal to good—evil is “spoiled good”; i.e., the perversion or corruption of goodness. Looking around the world, it is obvious that good has been corrupted into evil almost everywhere.

When Lewis was a much younger man, he found it impossible to believe in a just God who would allow Earth to become a sad, unjust place. However, the only way for an atheist to criticize the Christian model of God would be to appeal to some standard for “just” and “unjust”—i.e., the same standard that led us to accept the existence of God in Part One. Lewis then attempts to resolve the apparent contradiction in the existence of a good God who allows evil things to happen by arguing that God gives people the gift of free will: they face the challenge of behaving virtuously in spite of the temptations of evil—a challenge for which they will be richly rewarded in Heaven.

At the end of part two, Lewis introduces Jesus Christ, the cornerstone of the Christian religion. The only way to be truly virtuous, Lewis argues, is to worship Christ. While there are many different Christian sects that worship Christ in different ways, Lewis argues that they can agree on the basic facts about Christ’s existence, and therefore can all attain salvation.

Enemy-occupied territory—that is what this world is. Christianity is the story of how the rightful king has landed, you might say landed in disguise, and is calling us all to take part in a great campaign of sabotage. When you go to church you are really listening-in to the secret wireless from our friends: that is why the enemy is so anxious to prevent us from going. He does it by playing on our conceit and laziness and intellectual snobbery. I know someone will ask me, “Do you really mean, at this time of day, to reintroduce our old friend the devil—hoofs and horns and all?” Well, what the time of day has to do with it I do not know. And I am not particular about the hoofs and horns. But in other respects my answer is “Yes, I do.” I do not claim to know anything about his personal appearance. If anybody really wants to know him better I would say to that person, “Don’t worry. If you really want to, you will. Whether you’ll like it when you do is another question.” (46).

It is probably the same in the universe. God created things which had free will. That means creatures which can go either wrong or right. Some people think they can imagine a creature which was free but had no possibility of going wrong; I cannot. If a thing is free to be good it is also free to be bad. And free will is what has made evil possible. Why, then, did God give them free will? Because free will though it makes evil possible, is also the only thing that makes possible any love or goodness or joy worth having. A world of automata—of creatures that worked like machines—would hardly be worth creating. The happiness which God designs for His higher creatures is the happiness of being freely, voluntarily united to Him and to each other in an ecstasy of love and delight compared with which the most rapturous love between a man and a woman on this earth is mere milk and water. And for that they must be free. 47

The better stuff a creature is made of—the cleverer and stronger and freer it is—then the better it will be if it goes right, but also the worse it will be if it goes wrong. A cow cannot be very good or very bad; a dog can be both better and worse; a child better and worse still; an ordinary man, still more so; a man of genius, still more so; a superhuman spirit best—or worst—of all. 48

What Satan put into the heads of our remote ancestors was the idea that they could “be like gods”—could set up on their own as if they had created themselves—be their own masters—invent some sort of happiness for themselves outside God, apart from God. And out of that hopeless attempt has come nearly all that we call human history—money, poverty, ambition, war, prostitution, classes, empires, slavery—the long terrible story of man trying to find something other than God which will make him happy. 49

The reason why it can never succeed is this. God made us: invented us as a man invents an engine. A car is made to run on gasoline, and it would not run properly on anything else. Now God designed the human machine to run on Himself. He Himself is the fuel our spirits were designed to burn, or the food our spirits were designed to feed on. There is no other. That is why it is just no good asking God to make us happy in our own way without bothering about religion. God cannot give us a happiness and peace apart from Himself, because it is not there. There is no such thing. 49

I am trying here to prevent anyone saying the really foolish thing that people often say about Him: “I’m ready to accept Jesus as a great moral teacher, but I don’t accept His claim to be God.” That is the one thing we must not say. A man who was merely a man and said the sort of things Jesus said would not be a great moral teacher. He would either be a lunatic—on a level with the man who says he is a poached egg—or else he would be the Devil of Hell. You must make your choice. Either this man was, and is, the Son of God: or else a madman or something worse. You can shut Him up for a fool, you can spit at Him and kill Him as a demon; or you can fall at His feet and call Him Lord and God. But let us not come with any patronising nonsense about His being a great human teacher. He has not left that open to us. He did not intend to. 50-51

The central Christian belief is that Christ’s death has somehow put us right with God and given us a fresh start. Theories as to how it did this are another matter. A good many different theories have been held as to how it works; what all Christians are agreed on is that it does work. I will tell you what I think it is like. All sensible people know that if you are tired and hungry a meal will do you good. But the modern theory of nourishment—all about the vitamins and proteins—is a different thing. People ate their dinners and felt better long before the theory of vitamins was ever heard of: and if the theory of vitamins is some day abandoned they will go on eating their dinners just the same. Theories about Christ’s death are not Christianity: they are explanations about how it works. Christians would not all agree as to how important these theories are… A man can eat his dinner without understanding exactly how food nourishes him. A man can accept what Christ has done without knowing how it works: indeed, he certainly would not know how it works until he has accepted it (53).

There are three things that spread the Christ life to us: baptism, belief, and that mysterious action which different Christians call by different names—Holy Communion, the Mass, the Lord’s Supper. 57

Book 3: Christian Behaviour

In Book 3, Lewis studies the life of a good Christian. To begin with, Lewis proposes that morality consists of three different parts: harmony between people, harmony within a person, and constant vigilance in achieving a state of salvation. All virtues uphold the three parts of morality, and all sins contradict at least one of these parts.

In reality, moral rules are directions for running the human machine. Every moral rule is there to prevent a breakdown, or a strain, or a friction, in the running of that machine. That is why these rules at first seem to be constantly interfering with our natural inclinations. When you are being taught how to use any machine, the instructor keeps on saying, “No, don’t do it like that,” because, of course, there are all sorts of things that look all right and seem to you the natural way of treating the machine, but do not really work. 65

People often think of Christian morality as a kind of bargain in which God says, “If you keep a lot of rules I’ll reward you, and if you don’t I’ll do the other thing.” I do not think that is the best way of looking at it. I would much rather say that every time you make a choice you are turning the central part of you, the part of you that chooses, into something a little different from what it was before. And taking your life as a whole, with all your innumerable choices, all your life long you are slowly turning this central thing either into a heavenly creature or into a hellish creature: either into a creature that is in harmony with God, and with other creatures, and with itself, or else into one that is in a state of war and hatred with God, and with its fellow-creatures, and with itself. To be the one kind of creature is heaven: that is, it is joy and peace and knowledge and power. To be the other means madness, horror, idiocy, rage, impotence, and eternal loneliness. Each of us at each moment is progressing to the one state or the other. 81

After briefly discussing the four “Cardinal virtues”- prudence, temperance, justice, and fortitude, Lewis spends time defending the most unpopular aspect of Christian morality—the notion of chastity. Modern society, he insists, is overrun with sex and sexuality, to the point where people think that having lots of sex is “normal” and “healthy.”

Does it not make a great difference whether I am, so to speak, the landlord of my own mind and body, or only a tenant, responsible to the real landlord? If somebody else made me, for his own purposes, then I shall have a lot of duties which I should not have if I simply belonged to myself. 68

Lewis, however, argues that the sexual instinct—like any instinct—must be controlled and subdued. Lewis also defends the institution of marriage. While it’s popular to say that “being in love” is the only reason to get married, Lewis argues that being married is actually much more beautiful and majestic than being in love—a married couple must remain together for a lifetime, demonstrating their loyalty and respect for one another as human beings, rather than just following their emotions.

Lewis argues that pride is the most dangerous of all sins, since it encourages humans to place themselves “above God.” He suggests that many people who consider themselves to be good Christians actually worship a “false God,” and secretly think themselves to be superior to everyone else—a state of mind that will lead them to damnation unless they’re careful.

As long as you are proud you cannot know God. A proud man is always looking down on things and people: and, of course, as long as you are looking down, you cannot see something that is above you… The real test of being in the presence of God is that you either forget about yourself altogether or see yourself as a small, dirty object. It is better to forget about yourself altogether. 105

At the end of Part Three, Lewis discusses the three Theological virtues: charity, hope and faith. Charity is a challenging virtue, because it requires humans to be gracious and generous to people they might not necessarily like. But one of the miracles of virtue, Lewis claims, is that when we pretend to respect other people, we eventually do respect them. One of the most challenging aspects of Christianity, Lewis writes, is faith, especially in the challenging sense of having faith in God’s salvation. After a Christian becomes familiar with obeying the moral law of God, they sometimes reach a point of despair, during which they realize their own sinful nature. But even in their despair, the good Christian will find the strength to carry on, cautiously optimistic—not certain—that God will help them find the way to Heaven. A good Christian must trust their fate to God, while also working hard to be good.

Do not waste time bothering whether you “love” your neighbour; act as if you did. As soon as we do this we find one of the great secrets. When you are behaving as if you loved someone, you will presently come to love him…. Consequently, though Christian charity sounds a very cold thing to people whose heads are full of sentimentality, and though it is quite distinct from affection, yet it leads to affection. The difference between a Christian and a worldly man is not that the worldly man has only affections or “likings” and the Christian has only “charity.” The worldly man treats certain people kindly because he “likes” them: the Christian, trying to treat every one kindly, finds himself liking more and more people as he goes on—including people he could not even have imagined himself liking at the beginning… Good and evil both increase at compound interest. That is why the little decisions you and I make every day are of such infinite importance. 110-111

Some writers use the word charity to describe not only Christian love between human beings, but also God’s love for man and man’s love for God. About the second of these two, people are often worried. They are told they ought to love God. They cannot find any such feeling in themselves. What are they to do? The answer is the same as before. Act as if you did. Do not sit trying to manufacture feelings. Ask yourself, “If I were sure that I loved God, what would I do?” When you have found the answer, go and do it. 111

HOPE: If I find in myself a desire which no experience in this world can satisfy, the most probable explanation is that I was made for another world. If none of my earthly pleasures satisfy it, that does not prove that the universe is a fraud. Probably earthly pleasures were never meant to satisfy it, but only to arouse it, to suggest the real thing. If that is so, I must take care, on the one hand, never to despise, or be unthankful for, these earthly blessings, and on the other, never to mistake them for the something else of which they are only a kind of copy, or echo, or mirage. I must keep alive in myself the desire for my true country, which I shall not find till after death; I must never let it get snowed under or turned aside; I must make it the main object of life to press on to that other country and to help others to do the same.” 114

Book 4: Beyond Personality: Or First Steps in the Doctrine of the Trinity

In the fourth and final part of the book, Lewis turns to theology, the “science” of God.

Now, Theology is like the map. Merely learning and thinking about the Christian doctrines, if you stop there, is less real and less exciting than the sort of thing my friend got in the desert. Doctrines are not God: they are only a kind of map. But that map is based on the experience of hundreds of people who really were in touch with God—experiences compared with which any thrills or pious feelings you and I are likely to get on our own are very elementary and very confused. And secondly, if you want to get any further, you must use the map. 128

He analyzes the Holy Trinity, and the strange-sounding idea that God is both one thing and three.

Lewis compares the Holy Trinity to a die: just as a die “contains” six square sides, and yet is one three-dimensional object at the same time, so too does God “contain” three parts and yet remain one being.

Lewis also tackles the apparent contradiction of an all-knowing God who gives humans the gift of free will—one would think that, if God knows everything, then humans don’t truly choose their fates at all. Lewis resolves this apparent contradiction by arguing that God exists outside of time, meaning that he experiences humans’ past, present, and future in the same instant, whereas humans have free will within time as they experience it.

God is not hurried along in the Time-stream of this universe any more than an author is hurried along in the imaginary time of his own novel He has infinite attention to spare for each one of us. He does not have to deal with us in the mass. You are as much alone with Him as if you were the only being He had ever created. When Christ died, He died for you individually just as much as if you had been the only man in the world… If you picture Time as a straight line along which we have to travel, then you must picture God as the whole page on which the line is drawn. We come to the parts of the line one by one: we have to leave A behind before we get to B, and cannot reach C until we leave B behind. God, from above or outside or all round, contains the whole line, and sees it all. 138-9

Lewis goes on to write that, by worshipping Christ, humans can transcend their mortal nature and experience the divine life of Christ himself; put another way, by worshipping Christ, they, too, can become “sons of God.”

A man who changed from having Bios to having Zoe would have gone through as big a change as a statue which changed from being a carved stone to being a real man. And that is precisely what Christianity is about. This world is a great sculptor’s shop. We are the statues and there is a rumour going round the shop that some of us are some day going to come to life. 131

Good Christians unite together in their love for God—and yet they don’t sacrifice their individuality in doing so. On the contrary, Lewis argues, the only way to truly be an individual and fulfill one’s potential is to worship Jesus Christ. In the act of prayer, a human being assumes the guise of Jesus Christ; with practice and faith, prayer can help human beings become divine by leading them toward salvation in Heaven. In Heaven, people lose their desires for earthly things, and thus, the basic components of their so-called “personalities” on Earth. But in place of their old personalities, the saved discover their true selves: unique, individual, and yet united in love for God, in much the same way that the different organs of the human body are different from one another, and yet united in the facilitation of life. In short, Lewis argues, one must sacrifice one’s earthly needs and desires in order to be a Christian—but as a reward, one will find Christ, and rejoice in Heaven for eternity.

If we let Him—for we can prevent Him, if we choose—He will make the feeblest and filthiest of us into a god or goddess, a dazzling, radiant, immortal creature, pulsating all through with such energy and joy and wisdom and love as we cannot now imagine, a bright stainless mirror which reflects back to God perfectly (though, of course, on a smaller scale) His own boundless power and delight and goodness. The process will be long and in parts very painful; but that is what we are in for. Nothing less. He meant what He said. 163

Until you have given up your self to Him you will not have a real self. Sameness is to be found most among the most “natural” men, not among those who surrender to Christ. How monotonously alike all the great tyrants and conquerors have been: how gloriously different are the saints 176

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