What is it that makes discipleship authentic? Discipleship involves learning how to be in the world but not of the world. The first Christians were ambivalent about "the world": God so loved the world that he gave his only begotten son but friendship with the world is enmity with God. So discipleship involves learning how to live with this ambivalence and an ancient tension between loving and hating the world. This book offers a deeper understanding of what discipleship means by tracing the history of this ambivalence from the New Testament to the present. It presents a revisionary account of this history as a continuing and nonnegotiable tension between loving and hating the world rather than a simple transition from medieval world-denial to modern world-affirmation. It argues that this tension helped produce our own secular age and it considers modern Jewish and Christian philosophical and theological responses to this history that suggest ways that Christians can negotiate this tension to be more authentic disciples today.