C.S. Lewis’s Mere Christianity grew out of radio talks broadcast by the BBC during the Second World War. The talks were delivered in several series between 1941 and 1944 and were intended to explain basic Christian beliefs to a broad audience.
Lewis spoke without presenting a denominational system. Instead, he focused on themes such as morality, Christian doctrine, repentance, and the nature of God. The broadcasts were later revised and assembled into books, eventually forming the work known as Mere Christianity.
The title does not mean a vague or minimal religion. Lewis used “mere Christianity” for the shared core of belief held across historic Christian traditions. The work became one of his best-known apologetic books and helped establish his public reputation as a Christian broadcaster and writer.