Which C.S. Lewis book grew from radio broadcasts he gave during World War II?

Mere Christianity grew from radio broadcasts C.S. Lewis gave during World War II. The broadcasts were delivered for the BBC between 1941 and 1944 and were later revised and collected as a book.

Lewis was invited to explain basic Christian belief to a broad audience during a period of national crisis. His talks avoided arguing for one denomination and instead focused on ideas he regarded as shared by historic Christianity. The resulting book discusses morality, belief, Christian virtues, and the meaning of Christian doctrine.

The title refers to what Lewis called “mere Christianity,” meaning the central beliefs held across major Christian traditions. It does not mean a vague or diluted religion; Lewis intended the phrase to distinguish common doctrine from denominational disputes.

Mere Christianity is sometimes described as a direct transcript of the broadcasts. It is better understood as a revised book based on them, with changes made to wording, organization, and presentation for print.