Which C.S. Lewis book developed his wartime BBC radio talks on Christianity?

Mere Christianity developed C.S. Lewis’s wartime BBC radio talks on Christianity.

The talks were broadcast in Britain between 1941 and 1944, during the Second World War. Lewis presented arguments about morality, human nature, and Christian belief in a style intended for a broad radio audience rather than only academic specialists.

The later book was assembled from three related works: Broadcast Talks, Christian Behaviour, and Beyond Personality. The title Mere Christianity refers to the core beliefs shared across many historic Christian traditions, not to a separate denomination.

The book is sometimes mistaken for The Problem of Pain, another major Lewis work on Christianity. The Problem of Pain was published in 1940 and was not based on his BBC broadcasts. Mere Christianity became one of Lewis’s most influential nonfiction books.