During World War II, on January 11, 1942, C.S. Lewis began a second series of live broadcast talks over the BBC entitled What Christians Believe. As Walter Hooper notes, “Lewis could not assume that those listening to this series had heard his first one, and he began his broadcast…with this introduction:

It’s not because I’m anybody in particular that I’ve been asked to tell you what Christians believe. In fact it’s just the opposite. They’ve asked me, first of all because I’m a layman and not a parson, and consequently it was thought I might understand the ordinary person’s point of view a bit better. Secondly, I think they asked me because it was known that I’d been an atheist for many years and only became a Christian quite fairly recently. They thought that would mean I’d be able to see the difficulties – able to remember what Christianity looks like from the outside. So you see, the long and the short of it is that I’ve been selected for this job just because I’m an amateur not a professional, and a beginner, not an old hand. Of course this means that you may well ask what right I have to talk on the subject at all.”¹

In that same introduction, Lewis would go on to say, “What I’m going to say isn’t exactly what all these people (denominational leaders) would say, but the greater part of it is what all Christians agree on.…One thing I can promise you. In spite of all the unfortunate differences between Christians, what they agree on is still something pretty big and pretty solid: big enough to blow any of us sky-high if it happens to be true. And if it’s true, it’s quite ridiculous to put off doing anything about it simply because Christians don’t fully agree among themselves. That’s as if a man bleeding to death refused medical assistance because he’d heard that some doctors differed about the treatment of cancer. For if Christianity is true at all, it’s as serious as that.”²

C.S. Lewis’ great apologetic work, Mere Christianity, came from this and three other series of radio broadcasts. In his Preface, Lewis explains his own calling and the origin of the term “mere Christianity”:

Ever since I became a Christian I have thought that the best, perhaps the only, service I could do for my unbelieving neighbors was to explain and defend the belief that has been common to nearly all Christians at all times (emphasis added). I had more than one reason for thinking this. In the first place, the questions which divide Christians from one another often involve points of high Theology or even of ecclesiastical history which ought never to be treated except by real experts. I should have been out of my depth in such waters: more in need of help myself than able to help others. And secondly, I think we must admit that the discussion of these disputed points has no tendency at all to bring an outsider into the Christian fold. So long as we write and talk about them we are much more likely to deter him from entering any Christian communion than to draw him into our own. Our divisions should have already come to believe that there is one God and that Jesus Christ is His only Son. Finally, I got the impression that far more, and more talented, authors were already engaged in such controversial matters than in the defense of what Baxter calls ‘mere’ Christianity. That part of the line where I thought I could serve best was also the part that seemed to be the thinnest. And to it I naturally went.³

“Baxter” is none other than the great Puritan divine, Richard Baxter. In his Church History of the Government of Bishops (1680), he writes:

I am a CHRISTIAN, a MERE CHRISTIAN, of no other Religion; and the Church that I am of is the Christian Church, and hath been visible where ever the Christian Religion and Church hath been visible: But must you know what Sect or Party I am of? I am against all Sects and dividing Parties: But if any will call Mere Christians by the name of a Party, because they take up with Mere Christians, Creed, and Scripture, and will not be of any dividing or contentious Sect, I am of that Party which is so against Parties.⁴

Lewis is clear that he was “not writing to expound something I could call ‘my religion,’ but to expound ‘mere’ Christianity, which is what it is and was what it was long before I was born and whether I like it or not.”⁵ Apparently, from the beginning, the book was a success. “So far as I can judge from reviews and from the numerous letters written to me, the book, however faulty in other respects, did at least succeed in presenting an agreed, or common, or central, or ‘mere’ Christianity.”⁶

J.I. Packer has pointed out that presentations like C.S. Lewis’ Mere Christianity, Billy Graham’s Peace with God, John Stott’s Basic Christianity, and G.K. Chesterton’s Orthodoxy “are intended to instruct outsiders and establish insiders in fundamentals of the faith.”⁷ In 2006, another scholar wrote a book with the same purpose. Theologian N.T. Wright wrote:

I haven’t attempted in these pages to differentiate between the many different varieties of Christianity, but have tried to speak of that which is, at their best, common to all. The book isn’t ‘Anglican,’ ‘Catholic,’ ‘Protestant,’ or ‘Orthodox,’ but simply Christian. I have also attempted to keep what must be said as straightforward and clear as I can, so that those coming to the subject for the first time won’t get stuck in a jungle of technical terms.⁸

What, then, is a “mere Christian”? It is a person who has embraced the historic, simple, common Christian faith as communicated to the church by Christ through His Word and His Apostles. All true believers in the Lord Jesus Christ are “mere Christians.”