Which C.S. Lewis book grew out of his 1940s radio broadcasts on Christian belief?

Mere Christianity grew out of C.S. Lewis’s 1940s radio broadcasts on Christian belief.

Lewis first presented the material in a series of BBC radio talks during the Second World War. The broadcasts were intended for a broad public audience and explained shared Christian ideas rather than defending one denomination’s distinctive doctrines. Their conversational style helped make Lewis a widely recognized religious broadcaster.

The talks were later revised and published in book form. Mere Christianity is organized around themes such as morality, Christian belief, and the transformation of character. The title refers to the common core of traditional Christianity, not to a separate denomination.

The work is often confused with The Problem of Pain, another major apologetic book by Lewis. The Problem of Pain was published in 1940 and addresses suffering, while Mere Christianity developed from broadcast talks delivered during wartime Britain.