Which C.S. Lewis book presents Christian ideas through wartime radio talks?

Mere Christianity presents Christian ideas through material that began as C.S. Lewis's wartime radio talks. The BBC broadcast the talks during the Second World War, beginning in 1941, and Lewis later revised them for publication.

The book is organized around broad Christian themes rather than the distinctive doctrines of one denomination. Lewis discusses morality, belief, Christian conduct, and the meaning of the Christian life, aiming to explain shared principles in accessible language.

The title does not mean that the book is a neutral survey of every religion. “Mere Christianity” refers to what Lewis considered the common core of historical Christian belief. The final book appeared in 1952 after the broadcast material had been revised and combined.

The Problem of Pain, Miracles, and The Four Loves are also nonfiction books by Lewis, but they did not originate as this sequence of wartime BBC talks. Mere Christianity remains his most widely recognized apologetic work.