What is it that makes C.S. Lewis’s Mere Christianity so lastingly compelling? While most books fade in popularity, Lewis’s apologetic volume has sold even better in the twenty-first century than it did when it was first published. In English alone, it has reached something like four million copies since 2001. It is still the favorite go-to book for those considering Christianity or having doubts about their faith. New York Times columnist David Brooks quipped that when he was contemplating commitment to Christianity, acquaintances sent him about three hundred books, “only a hundred of which were different copies of C.S. Lewis’s Mere Christianity.”

Mere Christianity was not even originally written to be a book. It arose out of four sets of radio addresses that Lewis gave on the BBC during some very stressful years of World War II, from 1941 to 1944. Lewis had these published as separate little booklets soon after the broadcasts. But it was not until 1952 that he collected them into one volume with a new introduction as Mere Christianity.

Given the remarkable successes of this book, an edifying question to ask is, What were the qualities of Lewis’s communication of the faith that made it so lastingly effective? None of us is another C.S. Lewis, but each of us might learn from him how best to communicate our faith to others.

1. Lewis looked for timeless truths.

One of the strongest habits of thought both in Lewis’s day and in our own is to think that newer understandings of the most basic aspects of life and reality are better than older understandings. Lewis, as a student of history, recognized that many of the “latest ideas” of one’s own day will look quaint to future generations. When Lewis himself was on his journey to becoming a Christian, he came to realize that there was good reason to put one’s trust in ideas that had lasted a long time, rather than in the latest fads that would come and go.

He accordingly defined “mere Christianity” as “the belief that has been common to nearly all Christians at all times” (viii). Rather than presenting the latest modern ideas about Christianity, he was presenting an essential Christianity that had been around “long before I was born and whether I like it or not” (ix).

Grounding his presentation in history also meant that he carefully avoided presenting Christianity as a support for some currently fashionable social or political cause — as he put it, like “Christianity and Vegetarianism” or “Christianity and the New Order.” In The Screwtape Letters, the senior devil Screwtape advises the junior devil Wormwood to suggest to his “patient” (the young man who is in “danger” of becoming a true Christian) that Christianity is valuable chiefly for the excellent arguments it provides for the positions of his political party (135). Such partisanship, Screwtape suggests, would lead the young man away from considering the more essential issues.

“C.S. Lewis was careful to avoid efforts to improve Christianity with modern theological fads.”

Likewise, Lewis was careful to avoid efforts to improve Christianity with modern theological fads. These, he says, turn out to be versions of “Christianity and water” that dilute the essence of an essentially strong, life-changing drink. Unlike the liberal ecumenism that was so prominent in his day, which offered a largely demythologized Christianity, Lewis insisted on a robust appropriation of the central supernaturalist claims that have been the gospel message throughout the ages.

2. Lewis connected with perennial human nature.

Lewis’s lifelong quest for timeless truths led him not only to emphasize core Christian doctrines, but also to be able to reach wide audiences. As a student of the history of literature, he was alert to finding common traits of human nature, revealed in many guises in differing times and places. So when he was asked to speak on the BBC to quite literally every sort of person in England, he knew where to start — with common human experience.

He started by appealing to individuals’ own experiences of the perennial human conviction that there was a real right and wrong in the universe. Most people could recognize that other humans (the Nazis whom they were fighting, for instance) often egregiously failed to live up to proper standards of right and wrong. And if they were honest, they might see that they themselves did not always live up to those standards either. So, Lewis began by trying to cultivate a sense of guilt that was a necessary first step toward looking for a cure.

3. Lewis put reason in the context of the imagination.

One of the most striking features of Mere Christianity is its clarity of language — especially its effective uses of imagination, metaphor, and analogy. Sometimes people assume that Lewis was primarily a rationalistic apologist, and they dismiss him without much attention or even say that such rationality is out-of-date in the twenty-first century. But as many commentators have pointed out, while there are some conspicuous arguments in Mere Christianity, Lewis appeals more essentially to the imagination. As a literary person and writer, he understood reality through analogies and images. So, the Lewis of Narnia and his other imaginative works is also the Lewis of Mere Christianity.

Readers familiar with Mere Christianity may recall some of the many images that Lewis uses to describe becoming a Christian. It is like passing from death into life, or like laying down your rebel arms and surrendering, or like saying sorry, or like killing part of yourself, or like learning to walk or to write, or like buying God a present with his own money. Or it is like a drowning man clutching at a rescuer’s hand, or like a tin soldier or a statue becoming alive, or like a horse turning into a Pegasus, or like a compass needle swinging to north, or like a dark greenhouse transformed as the roof suddenly becomes bright in the sunlight. And many more.

4. “Mere” Christianity involved a demanding gospel message.

Lewis was not promoting “cheap grace” — to use the term that Dietrich Bonhoeffer coined in the same era. “Mere” Christianity is not minimal Christianity. It is not easy or safe. Rather, readers find that they are being drawn in to an understanding of Christianity that is going to be extraordinarily demanding on them personally.

They are being asked to give up their very “self” as a sovereign entity, and to experience Christ living in them. “To become new men means losing what we now call ‘ourselves.’ Out of our selves, into Christ, we must go” (224). Elsewhere he writes, “This is the whole of Christianity. There is nothing else. . . . The Church exists for nothing else but to draw men into Christ, to make them little Christs” (199). We are being made into creatures who can obey the command, “Be ye perfect” (198). We are to be transformed “from being creatures of God to being Sons of God” (220). That is possible only by being “in Christ,” who is the first instance of this new humanity. So, there must be “a real giving up of the self” (226).

“‘Mere’ Christianity is not minimal Christianity. It is not easy or safe.”

The demands of giving up the liberties of self-rule to be “in Christ” have sometimes been obscured in the popular revivalist traditions, where being “born again” may be presented as a sort of magical moment based on one’s “decision for Christ,” as though we are still in control. For Lewis the emphasis is more clearly on seeking to be open to being “surprised by joy,” as he puts it in the title of his spiritual autobiography. Recognition of the beauty that brings that joy leads to the otherwise impossible submission of the self. Being “in Christ” means a radical reordering of one’s loves, as in the Augustinian tradition. We find ourselves in the orbit of the sun of Christ’s love so that our own loves begin to be brought into their proper places. We seek to love what God loves.

5. Lewis pointed readers to the luminosity of the gospel message itself.

In 1939 Lewis published an essay on “The Personal Heresy” in literary criticism. He argued that it was wrong to view a poem as about the poet’s state of mind. “The poet is not a man,” he wrote, “who asks me to look at him; he is a man who says ‘look at that’ and points; the more I follow the pointing of his finger the less I can possibly see of him” (14).

Lewis would have said the same for his work as an apologist. Had it drawn primary attention to himself, or have been just a reflection of his own peculiar views, it would have had little lasting impact. In fact, one of the greatest sources of the lasting vitality of the presentations is that Lewis deliberately points the listener or reader toward an object.

As others have observed, he does not simply present arguments; rather, he acts more like a friendly companion on a journey. To expand on that image, he is like a companion on a hike who is an expert naturalist and who points out all sorts of flora or tiny flowers or rock formations that you would have missed on your own. And if your guide leads you to see one of the most astonishing views of mountain peaks and distant lakes that you have ever seen, you will be duly grateful to him. Yet the most unforgettable part of the experience arises from the power of beauty that you have been led to see.