And God said unto Moses,
I AM THAT I AM:
and he said,
Thus shall you say unto the children of Israel, I AM has sent me unto you.
All Commentaries on Exodus 3:14 Go To Exodus 3
Augustine of Hippo
AD 430
But God is without doubt a substance, or perhaps essence would be a better term, which the Greeks call ousia. For just as wisdom is so called from being wise and knowledge is so called from knowing, so essence is so called from being [esse]. And who possesses being in a higher degree than he, who said to his servant Moses, “I am who I am” and “He who is has sent me to you.” But all other things that are called essences or substances are susceptible of accidents, by which a change, whether great or small, is brought about in them. But there can be no accidents of this kind in God. Therefore only the essence of God, or the essence which God is, is unchangeable. .
