Which 1942 book by C.S. Lewis presents Christian arguments adapted from wartime radio broadcasts?

Mere Christianity is the 1942 book by C.S. Lewis presenting Christian arguments adapted from wartime radio broadcasts.

Lewis first delivered the material in a series of BBC radio talks during the Second World War. The broadcasts were later revised and assembled into book form. The work explains what Lewis calls “mere Christianity,” meaning the core beliefs shared across historic Christian traditions, rather than the distinctive doctrines of one denomination.

The book is arranged in four sections: “Right and Wrong as a Clue to the Meaning of the Universe,” “What Christians Believe,” “Christian Behaviour,” and “Beyond Personality.” It is sometimes incorrectly described as a transcript of one uninterrupted broadcast series; Lewis revised the talks for publication, and the book’s final structure reflects that editing.