Mere Christianity is a theological book by C. S. Lewis, adapted from a series of BBC radio talks made between 1942 and 1944, while Lewis was at Oxford during World War II. Considered a classic of Christian apologetics, the transcripts of the broadcasts originally appeared in print as three separate pamphlets: The Case for Christianity (1942), Christian Behaviour (1943), and Beyond Personality (1944). Lewis was invited to give the talks by Rev.