Lewis's 1952 Mere Christianity—originally printed in pamphlet form during World War II—documents a complex journey from atheism to faith. Lewis's fresh, lively, and often humorous presentation of Christian doctrine helped to make him arguably the greatest defender of Christianity of the 20th century. Challenging the modernism and naturalism of its day, the book demonstrated that an 'amateur' theologian, with a simple and straightforward style, could bring to life the fundamentals of Christian doctrine—even in a culture that increasingly dismissed the value of faith and the Church.