Which C.S. Lewis book adapts his BBC radio talks into Christian apologetics?

Mere Christianity adapts C.S. Lewis’s BBC radio talks into a work of Christian apologetics.

Lewis delivered the original talks during the Second World War, beginning in 1941. The broadcasts were intended for a general audience rather than specialist theologians, and they explained shared Christian ideas in accessible language. Lewis later revised and combined the material into book form.

The title refers to what Lewis presented as common or “mere” Christianity: beliefs shared across major Christian traditions. The book is organized into four parts, covering moral law, Christian belief, Christian behavior, and the doctrine of the Trinity. It became one of Lewis’s most influential nonfiction works.

The book is sometimes mistaken for The Problem of Pain, which is also apologetic but addresses suffering and divine goodness. Mere Christianity has a different origin: it grew directly from wartime radio broadcasts made for the BBC.