Which Christian apologetics book grew out of C.S. Lewis’s BBC radio talks?

Mere Christianity grew out of C.S. Lewis’s BBC radio talks broadcast during the Second World War. The talks were delivered between 1941 and 1944 and later revised and collected as a book.

Lewis designed the broadcasts to explain central Christian beliefs to a general audience rather than to argue for one particular denomination. The resulting book discusses morality, belief, Christian doctrine, and the meaning of conversion in accessible language.

The title refers to what Lewis viewed as common or “mere” Christianity: beliefs shared across major Christian traditions. The work is not a neutral survey of every church, and it does not attempt to settle all denominational differences. Its structure came from spoken talks, which helps explain its direct, conversational style.

Mere Christianity is sometimes confused with The Problem of Pain, another major Lewis apologetics work. The Problem of Pain was published in 1940 and addresses suffering, while Mere Christianity developed from wartime broadcasts aimed at a broad listening public.