C.S. Lewis's work arguing for common Christian ground among denominations is Mere Christianity.
Mere Christianity developed from radio broadcasts Lewis gave during the Second World War. The talks were later revised and published in book form, with the title referring to the central beliefs shared by Christians across denominational boundaries. Lewis discusses morality, belief, Christian doctrine, and the practical implications of faith.
The book is not intended as a complete account of every church’s distinctive teachings. Instead, Lewis presents what he regards as the basic or “mere” Christianity that lies behind disagreements between traditions. This focus helped make the work accessible to a broad English-speaking audience.
Its origins in wartime broadcasting also shaped its direct style. Lewis aimed to explain difficult religious ideas in ordinary language, often using analogies and structured arguments. The book remains one of his most widely read works of Christian apologetics.