The BBC invited C.S. Lewis to give the radio talks later published as Mere Christianity. Lewis delivered the talks during the Second World War, beginning in 1941, when the BBC was using radio to address a large British audience during national crisis.
The broadcasts were designed to explain central Christian beliefs in accessible language rather than to promote one denomination. Lewis’s talks were later revised and collected in book form. The title Mere Christianity refers to the shared core of beliefs held across many historic Christian traditions.
Mere Christianity is often described as a single book written all at once, but it developed from a sequence of broadcast talks and later printed collections. It followed Lewis’s earlier BBC broadcasts, including The Case for Christianity. The work became one of his most widely read Christian apologetic books and helped establish his public reputation as a communicator of religious ideas.