Book excerpt: When people encounter an argument for or against God's existence, it often raises more questions than it answers. In Letters to Doubting Thomas, C. Stephen Layman offers a fresh, insightful approach to the issue of God's existence--a way to organize what can seem like a blizzard of claims and concepts--bringing clarity to a debate often mired in confusion. Layman explores the evidence for the existence of God in a series of fictionalized letters between two characters--Zachary, a philosopher, and Thomas, an old college friend who appeals to Zach for help in sorting out his thoughts about God. As their correspondence grows, Zachary leads Thomas through an informal and highly readable comparison of Naturalism (the belief that there is no God and that ultimate reality is physical reality), and Theism (the idea that there is an almighty, perfectly good God). In engaging letters that break down complex philosophical arguments into easily digestible bits, the two friends delve into such weighty topics as the reliability of religious experience, various arguments for God's existence (such as the cosmological, design, and moral arguments), the question of free will, and the problem of evil. A piece at a time, they build an argument that shows that Theism, on balance, provides a better explanation of the world and human life than does Naturalism. Here then is a highly accessible account of the major arguments for and against the existence of God, capturing some of the best new insights of modern philosophy in a marvelously clear and engaging format.