This chapter takes a closer look at three figures whose discussions of faith are among the most influential in twentieth-century Christian theology. Two, Paul Tillich and Karl Barth, are twentieth-century Christian theologians and one, Søren Kierkegaard, is a nineteenth-century philosopher, but all three determine directions taken by existentialist Christian theology in the late twentieth century. All three figures happen to be Protestant, not simply by denominational identification, but more importantly, each is guided by the Protestant doctrine of justification by faith alone to emphasize the priority of God's saving grace over any human works and human understanding. All three adhere to the Protestant Principle (an individual's right and responsibility to radically question and reinterpret questions of faith), albeit in different ways.