Despite my failures to comprehend C. S. Lewis’s argument for the existence of God, I have always appreciated his account of common Christian beliefs and practices: that’s what he meant by “mere Christianity.” Lewis wrote Mere Christianity at the zenith of twentieth-century optimism about Christian unity. He arrived at his conclusions about common Christian beliefs and practices partly by intuition, partly by his immense knowledge of medieval European culture, and partly by running his stuff about common beliefs by Catholic, Anglican, Presbyterian, and Methodist clergymen. Originally a series of radio talks that aired during the Second World War, the book was published in 1952, four years after the organizational meeting of the World Council of Churches. Lewis was not directly in touch with leaders of the movement for Christian unity, the ecumenical movement, but he seems to have imbibed the ecumenical spirit of the age and he thought he could write something up, run it by four clergymen, and then present readers with the essence of common Christianity. In my estimation he did a good job of that.
We do not live in such an age. Optimism for Christian unity has long since faded. The ecumenical movement now appears as a Christian expression of a particular era in western culture that valued modern visions of global unity, stripped of their moorings in traditional cultures, in art and architecture and music and political organization. That vision is now deeply suspect and likely to be seen as a relic of a bygone era even as ugly buildings in the “International Style” grow increasingly decrepit. Some of its most obvious expressions, like the Union of Soviet Socialist Republics, have altogether disappeared. Others persist, like the United Nations and the World Bank, but today these groups project more the aura of staid institutional structures than that of vibrant and popular movements for human progress. Theologians and historians today speak readily of multiple and divergent “christianities,” presupposing or stating as a dogmatic principle that there are not and have never been common Christian practices and beliefs except perhaps at the most superficial level. So discerning “mere” Christianity isn’t as easy today as C. S. Lewis imagined it to be in the 1940s.