Which C.S. Lewis book developed from his 1941–1944 BBC radio talks on Christianity?

C.S. Lewis’s Mere Christianity developed from his 1941–1944 BBC radio talks on Christianity. The broadcasts were aimed at a general audience during the Second World War and sought to explain shared Christian ideas in accessible language.

Lewis did not originally deliver the material as a single book. He revised and expanded the broadcasts into separate parts, later collected as Mere Christianity. The work discusses moral law, Christian belief, and the central doctrines held across major Christian traditions.

The title refers to what Lewis considered the common ground of historic Christianity rather than the distinct teachings of one denomination. Because the book grew from radio talks, its prose often retains a conversational tone. It is not the same work as The Problem of Pain, Lewis’s earlier book on suffering.