What was C.S. Lewis’s BBC-based book of Christian apologetics called?

C.S. Lewis’s BBC-based book of Christian apologetics is called Mere Christianity.

The book grew out of radio talks Lewis delivered for the BBC during the Second World War, mainly between 1941 and 1944. The broadcasts addressed ordinary listeners and explained central Christian ideas in accessible language. Lewis later revised and combined the talks into a book published in 1952.

Mere Christianity does not present the distinctive doctrines of one denomination. Instead, Lewis aimed to describe what he regarded as the shared core of historic Christianity. The work is organized into discussions of morality, Christian belief, and Christian conduct. It is often confused with The Problem of Pain, another apologetic book by Lewis, but that earlier work focuses more specifically on suffering and the existence of God. Mere Christianity became one of Lewis’s most widely read religious books.