Reason for God : Conversations on Faith and Life: Discussion Guide, Six Lessons, Paperback by Keller, Timothy, ISBN 0310330475, ISBN-13 9780310330479, Brand New, Free shipping in the US This six-session small group Bible study, The Reason for God, captures live and unscripted conversations between Tim Keller and a group of people to address their doubts and objections to Christianity. Throughout, Keller and the group explore the truth of Christianity.