Wilber has given us the secret of the ages – in sublime simplicity.
Wilber came to this exquisite understanding via the mystics and Buddhism. Paul Tillich came to the same understanding via the words and concepts route as in this explanation;
Tillich defines faith, and indirectly religion, as "ultimate concern." Religion is direction or movement toward the ultimate or the unconditional And God rightly defined might be called the Unconditional. God, in the true sense, is indefinable. Since the Unconditional precedes our minds and precedes all created things, God cannot be confined by the mind or by words. Tillich sees God as Being-Itself, or the "Ground of all Being." For this reason there cannot be a God.
There cannot even be a "highest God," for even that concept is limiting. We cannot make an object out of God. And the moment we say he is the highest God or anything else, we have made him an object.
Thus, beyond the God of the Christian or the God of the Jews, there is the "God beyond God." This God cannot be said to exist or not to exist in the sense that we exist. Either statement is limiting. We cannot make a thing out of God, no matter how holy this thing may be, because there still remains something behind the holy thing which is its ground or basis, the "ground of being."