Which Christian book by C.S. Lewis originated as radio talks broadcast during World War II?

Mere Christianity originated as radio talks and became C.S. Lewis’s book Mere Christianity.

The talks were broadcast by the BBC during World War II, beginning in 1941. Lewis presented a series of accessible arguments about Christian belief, morality, and the idea of a shared “mere” Christianity rather than focusing on disputes between denominations.

The broadcasts were later revised and published in book form. The title Mere Christianity refers to the core beliefs Lewis believed were held across the major Christian traditions. The work became one of his most widely read pieces of Christian apologetics.

The book is sometimes confused with The Problem of Pain, which Lewis published in 1940 as a study of suffering, or with The Four Loves, published in 1960. Mere Christianity is specifically linked to wartime radio broadcasting and is therefore distinct in origin as well as subject.