" if, when you think of the word “God,” you are thinking of a reality that may or may not exist, you are not thinking of God. Tillich’s point is that the word “God” does not refer to a particular existing being (that’s the God of supernatural theism). Rather, the word “God” is the most common Western name for “what is,” for “ultimate reality,” for “the ground of being,” for “Being itself,” for “isness. "

― Marcus J. Borg , The Heart of Christianity: Rediscovering a Life of Faith