April 9, 2007 issue - Rick Warren is as big as a bear, with a booming voice and easygoing charm. Sam Harris is compact, reserved and, despite the polemical tone of his books, friendly and mild. Warren, one of the best-known pastors in the world, started Saddleback in 1980; now 25,000 people attend the church each Sunday. Harris is softer-spoken; paragraphs pour out of him, complex and fact-filled—as befits a Ph.D. student in neuroscience. At NEWSWEEK's invitation, they met in Warren's office recently and chatted, mostly amiably, for four hours. Jon Meacham moderated. Excerpts follow....