Which C.S. Lewis book developed ideas from his wartime BBC broadcasts on Christianity?

Mere Christianity developed ideas from C.S. Lewis’s wartime BBC broadcasts on Christianity.

Lewis delivered the first series of talks in 1941, followed by additional broadcasts in 1942 and 1944. The talks were intended for a broad British audience during World War II, and Lewis used clear, conversational language rather than technical theological terminology. He discussed morality, belief, Christian behavior, and the shared core of historic Christianity.

The broadcasts were later revised and gathered into book form. Mere Christianity was published in 1952 and became one of Lewis’s most influential works of Christian apologetics. Its title refers to the common central beliefs shared by the major Christian traditions, not to a new denomination founded by Lewis.

A frequently cited section is Lewis’s argument that Jesus cannot be treated merely as a great moral teacher if one accepts the claims attributed to him. The book also includes the famous “Lord, liar, or lunatic” discussion, although Lewis’s overall argument is broader than that short formula. The work grew from radio talks, but the final book is edited and organized rather than being a verbatim transcript.