Which C.S. Lewis book grew out of his wartime radio broadcasts about Christianity?

Mere Christianity grew out of C.S. Lewis’s wartime radio broadcasts about Christianity.

The book was published in 1952, but its origins were broadcasts Lewis delivered for the BBC during the Second World War. The talks were intended for a broad British audience and presented a basic case for Christian belief without focusing on differences between denominations.

Lewis revised the broadcast material into three earlier works: Broadcast Talks, Christian Behaviour, and Beyond Personality. Mere Christianity brought that material together in a single volume. Its opening argument begins with everyday ideas about right and wrong, then develops toward questions about human nature, morality, and Christian belief.

The book is sometimes described as a transcript of one uninterrupted radio series. In fact, Lewis gave several sets of talks between 1941 and 1944, and the published text was edited and reorganized. It also should not be confused with The Case for Christianity, an earlier American compilation of related material.