What was the name of C.S. Lewis’s Christian apologetics book based on his BBC talks?

C.S. Lewis’s Christian apologetics book based on his BBC talks was Mere Christianity.

The book developed from radio broadcasts Lewis delivered for the BBC between 1941 and 1944. The talks were aimed at a general wartime audience and explained common Christian ideas without focusing on one denomination. Lewis later revised and combined the material for publication.

Mere Christianity is organized around a shared core of Christian belief. It includes Lewis’s discussion of morality, human behavior, repentance, and the Christian understanding of God. The work became one of his most widely read nonfiction books.

The title does not mean that Lewis was arguing for a vague religion. “Mere Christianity” refers to beliefs shared across many historic Christian traditions. The book is therefore distinct from The Problem of Pain, which focuses on suffering, and Miracles, which examines the possibility of supernatural events.