The BBC first aired the talks later collected as C.S. Lewis’s Mere Christianity. Lewis delivered a series of radio broadcasts for the British Broadcasting Corporation during the Second World War.
The broadcasts were designed to explain core Christian ideas in clear, accessible language rather than to promote a particular denomination. Lewis spoke without a prepared script in the style of a direct radio address, which helped make the material understandable to a broad audience.
The talks were later revised and combined into the book Mere Christianity. The title refers to the shared central beliefs of historic Christianity, not to a new church or denomination. The book is divided into sections that discuss morality, Christian belief, and Christian conduct.
The broadcasts made Lewis widely known beyond academic and literary circles. They also helped establish the conversational apologetic style that became one of his defining features as a religious writer.