In demonstrating the courage to be, Tillich believes that we are affirming ourselves in the face of non-being. The anxiety of non-being is ever-present, and in order to overcome it, we need to assert our being; that is, we need to have the courage to be.
In Tillich's thought, anxiety is a general condition, unrelated to any specific thing. But it arises from a loss of spirituality, a common condition in the secular age in which we live. Anxiety over the threat of non-being deprives us of a sense of purpose in life, making our whole existence, and the world in which he have that existence, seem utterly meaningless.
In confronting anxiety in a resolute manner, in taking on the ever-present threat of non-being, we display the courage to be. We do this by the twin processes of true faith and self-affirmation. The courage to be, then, has a recognizably religious foundation to it, whether we choose to acknowledge it or not.
For Tillich, God is Being, something higher than the anthropomorphic God of traditional theism. By asserting ourselves and thus assessing our being, we are therefore partaking of something higher, what Tillich calls a God above God, which transcends the conception of God as traditionally understood.