Chapter 11 — That God’s essence is not other than his existence

Furthermore, God’s essence cannot be other than his existence. In any being whose essence is distinct from its existence, the being must be by one thing and be something by another thing. For in virtue of a thing’s existence we say that it is, and in virtue of its essence we say what it is. This is why a definition that signifies an essence manifests what a thing is. In God, however, there is not one thing by which he exists, and another by which he is something, since there is no composition in him, as has been shown. Therefore, God’s essence is nothing else than his existence.

Again, we have proved that God is pure act without any admixture of potentiality. Accordingly, his essence must be ultimate act; for any act that is short of the ultimate act is in potency to that ultimate act. But the ultimate act is being itself. For, since all motion is an issuing forth from potency to act, the ultimate act must be that toward which all motion tends; and since natural motion tends to what is naturally desired, the ultimate act must be that which all desire. This is being. Consequently, the divine essence, which is pure and ultimate act, must be being itself.