Mere Christianity by C.S. Lewis is the most popular of his works.
This book, Mere Christianity by C.S. Lewis, brings together Lewis's legendary radio broadcast talks in which he set out simply "to explain and defend the belief that has been common to nearly all Christians at all times".
Rejecting the boundaries that divide Christianity's many denominations, Mere Christianity by C.S. Lewis is his term for the essential Christian message, the theological core on which diverse Christian traditions can stand together.
Mere Christianity by C.S. Lewis definitely speaks to the ecumenical spirit of contemporary times.