Which C.S. Lewis book presents Christianity through radio talks later adapted into essays?

Mere Christianity presents C.S. Lewis’s Christian ideas through material first delivered as radio talks.

The talks were broadcast by the BBC during the Second World War, beginning in 1941. Lewis spoke about basic Christian beliefs in language intended for a broad audience rather than addressing a single denomination. The talks were later revised and published in book form, with Mere Christianity appearing as a collected work in 1952.

The title refers to what Lewis regarded as the shared core of Christianity rather than the distinctive practices of particular churches. Its discussions include morality, belief, Christian virtues, and the claims of Christian faith. The book became one of his best-known works of Christian apologetics.

Readers sometimes assume the book was originally written as a conventional treatise. Its broadcast origin explains its conversational tone and accessible structure. It also places the work within wartime Britain, when radio allowed Lewis to reach listeners far beyond the Oxford academic world.