The original title of C.S. Lewis’s 1954 book about Christian belief was Mere Christianity.
The book developed from radio broadcasts Lewis gave for the BBC during the Second World War. The talks were first published in separate collections, including Broadcast Talks and Christian Behaviour, before being revised and gathered as Mere Christianity in 1952 in Britain and 1954 in the United States.
Lewis presented the work as a defense of shared Christian beliefs rather than as an explanation of one denomination’s distinctive teachings. Its opening discussion of morality and the later treatment of central Christian doctrines made it one of his most widely read apologetic works.
The word “mere” means basic or common Christianity in this context, not an attempt to dismiss the subject as unimportant. That wording is a frequent source of misunderstanding when the title is encountered without its historical context.