The German philosopher Martin Heidegger (1889–1976) is one of the most influential and controversial figures in twentieth century intellectual history. Though it is well known that his brand of phenomenology was heavily indebted to Christian theology, the specific terms of this debt, its impact on his shifting views of time, subjectivity and selfhood, as well as its role in his rejection of modern metaphysics have not been fully grasped. Drawing upon new evidence, this book argues that Heidegger’s initial confrontations with the apostle Paul and with Augustine of Hippo’s Confessions in the years leading up to Being and Time (1927) generated a series of tensions running throughout his work from start to finish. Though concepts drawn from these sources informed Being and Time, they also worked at cross-purposes with its ultimate philosophical aims. Starting in 1930 Heidegger sought to revise these concepts in part by reconsidering their textual sources. This book argues that in his later writings Heidegger reused concepts originally drawn from his 1921 and 1930 seminars on Augustine to criticize his earlier views while simultaneously deepening his criticism of the metaphysical tradition from the pre-Socratic philosophers to Friedrich Nietzsche. It also contends that Heidegger’s complex use of theological sources, coupled with his repeated attempts to distance his own thinking from Christian theology, is instructive for philosophy and religious studies alike, as it can help us to clarify the primary object of inquiry for what is often called the philosophy of religion.