Which Christian apologetics book by C.S. Lewis grew from wartime radio broadcasts?

C.S. Lewis’s Mere Christianity grew from wartime radio broadcasts. The original talks were delivered for the BBC during the Second World War, beginning in 1941, and were later revised and published in book form.

The work presents a broad case for basic Christian beliefs rather than defending one denomination. Lewis organized it into four books: “Right and Wrong as a Clue to the Meaning of the Universe,” “What Christians Believe,” “Christian Behaviour,” and “Beyond Personality.” Its conversational style helped make difficult theological ideas accessible to a large audience.

A common misconception is that Mere Christianity is a transcript of a single radio lecture. It is instead a compiled and revised version of several broadcast series. Lewis’s “trilemma” concerning Jesus—often summarized as Lord, liar, or lunatic—became one of the most frequently discussed passages, although the book’s argument covers morality, faith, and Christian practice much more broadly.