Which C.S. Lewis work originated as radio broadcasts on Christianity during World War II?

Mere Christianity originated as C.S. Lewis’s radio broadcasts on Christianity during World War II.

The BBC invited Lewis to give a series of talks for radio audiences in Britain. The broadcasts began in 1941, continued in later series, and were eventually revised into the book Mere Christianity. The title refers to the shared core of belief that Lewis believed was held across historic Christian traditions, rather than to a separate denomination.

Lewis organized the material around moral law, Christian belief, and the practical implications of faith. His conversational style helped make complex arguments accessible to listeners who might not attend a university lecture or read a theological treatise. The finished book is therefore related to, but not identical with, the original broadcasts.

The work is sometimes confused with The Case for Christianity, an earlier book that drew on the first broadcast series. The later Mere Christianity combines material from all three broadcast series and adds revisions. It is also distinct from The Problem of Pain, which focuses more directly on suffering and divine goodness.