Which C.S. Lewis book presents his BBC wartime broadcasts as Christian apologetics?

Mere Christianity presents C.S. Lewis’s BBC wartime broadcasts as Christian apologetics.

The book developed from radio talks Lewis delivered for the BBC during the Second World War, beginning in 1941. The talks were intended for a broad audience rather than specialists, and they explained shared Christian beliefs while avoiding detailed divisions between denominations. Lewis revised and expanded the broadcasts before they appeared in book form.

The title refers to what Lewis regarded as the common or central core of Christianity, not to a separate denomination. Readers sometimes assume the book was written as a conventional academic theology textbook; its origins in radio shaped its conversational style and accessible explanations. The Problem of Pain and Miracles are related Lewis works, but neither is the collected book based on the BBC broadcasts.