Which C.S. Lewis book developed ideas from his wartime radio broadcasts?

Mere Christianity developed ideas from C.S. Lewis’s wartime radio broadcasts. The broadcasts were delivered for the BBC between 1941 and 1944 and later revised into a book.

Lewis designed the talks to explain basic Christian beliefs to a broad British audience during the Second World War. He aimed to discuss what he called “mere” Christianity: beliefs shared across many historic Christian traditions.

The book is organized around moral law, Christian doctrine, and practical belief. It includes Lewis’s famous argument that Jesus cannot simply be regarded as a great moral teacher if his claims about himself are taken seriously.

Mere Christianity is sometimes confused with The Problem of Pain or Miracles, which address related theological subjects. It is specifically the book connected to the BBC talks known as Broadcast Talks and Christian Behaviour.