Which C.S. Lewis book adapts his 1940s radio talks on Christian belief?

Mere Christianity adapts C.S. Lewis’s 1940s radio talks on Christian belief.

The talks were broadcast by the BBC during World War II, beginning in 1941. Lewis spoke to a broad British audience and presented arguments about morality, human behavior, and the basic beliefs shared by historic branches of Christianity.

The broadcasts were later revised and collected in book form. The title Mere Christianity refers to the common core of Christian belief rather than to one denomination’s distinctive doctrines.

The book is often confused with The Problem of Pain, another major Lewis work on Christianity. The Problem of Pain focuses particularly on suffering and divine goodness, whereas Mere Christianity grew directly from the radio talks and offers a broader apologetic presentation.