Not long after his rather dramatic conversion to Christ, in 1929, the late C. S. Lewis wrote to a friend: “When all is said (and truly said) about the divisions of Christendom, there remains, by God’s mercy, an enormous common ground.” My bedrock conviction, and that of ACT 3, is that Lewis was right, profoundly right. This enormous common ground should be discussed, reconsidered and taught. Christians need to know that "core orthodoxy" is a reality and that holding to it really matters a great deal. It is here, as Lewis argued so often, that we find the central truth of Christianity, the truth that unites all who know Christ as Lord.
Walter Hooper notes, in his preface to Christian Reflections (Eerdmans, 1967): “From that time (i.e. 1929) on Lewis thought that the best service he could do for his unbelieving neighbors was to explain and defend the belief that has been common to nearly all Christians at all times—that ‘enormous common ground’ which he usually referred to as ‘mere’ Christianity.”
Lewis held views that many of us disagree with heartily. His understanding of the nature of divine inspiration troubles some. His conclusion on certain issues that come from reading the biblical text still troubles some evangelicals. (He was not a theologian, but a professor of English literature who became an evangelist and Christian apologist.) But Lewis was always a thoroughgoing supernaturalist in a time when many in the Church of England were expressing great doubt. He believed in the basic Christian doctrines of creation, fall, the incarnation and the four last things (death, judgment, heaven and hell).
Walter Hooper says the thing that singularly set Lewis apart from many others was his total confidence in the immortality of all mankind. Lewis really believed that there was a heaven and a hell. This was an important ingredient in his understanding of “mere” Christianity. (By “mere” Christianity Hooper says he believed in “pure” Christianity and in another place Lewis referred to his views as those that were a part of “deep church.”)
Lewis spoke of hell enough that some accused him of being preoccupied with it. Such is not the case. Hooper says, “For him the real problem was: so much mercy, yet still there is hell. Regardless of what we all wish Christianity were, he knew this terrible doctrine has the support of Scripture (especially of our Lord’s own words) as well as that of reason: ‘If a game is played, it must be possible to lose it.’”
Mere Christianity is not some kind of “weak kneed” orthodoxy for those who want to deny the essential elements of Christianity. It is “true” and “deep” and is established by faith in basic teachings of the Scripture. And it can bring Christians together in powerfully important ways.