Exodus 3:14

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.

For although that immutable and ineffable nature does not admit of was and will be but only is (for it truly is, because it cannot be changed), and therefore it was proper for him to say, "I am who I am" and "You will say to the children of Israel, 'He who is has sent me to you,' " nevertheless, on account of the changeableness of the times in which our mortality and our changeableness are involved, we do not falsely say was and will be and is. Was, in past ages; is, in present ones; will be, in future ones. Was, because he was never lacking; will be, because he will never be lacking; is, because he always is.

Christ therefore is and always is; for he who is, always is. And Christ always is, of whom Moses says, "He that is has sent me."

That the activity of the Father and the Son is to be found both in saints and in sinners is clear from the fact that all rational beings are partakers of the word of God, that is, of reason, and so have implanted within them some seeds, as it were, of wisdom and righteousness, which is Christ. And all things that exist derive their share of being from him who truly exists, who said through Moses, "I am that I am"; which participation in God the Father extends to all, both righteous and sinners, rational and irrational creatures and absolutely everything that exists.

Everything that has ever existed or now exists derives its being from the One, the only existent and preexistent being, who also said, "I am the existent." … As the only being and the eternal being, he is himself the cause of existence to all those to whom he has imparted existence from himself by his will and his power and gives existence to all things and their powers and forms, richly and ungrudgingly from himself.

While my mind was dwelling on these and on many like thoughts, I chanced upon the books which, according to the tradition of the Hebrew faith, were written by Moses and the prophets, and found in these words spoken by God the Creator testifying of Himself `I Am that I Am, and again, He that is hath sent me unto you.' I confess that I was amazed to find in them an indication concerning God so exact that it expressed in the terms best adapted to human understanding an unattainable insight into the mystery of the Divine nature. For no property of God which the mind can grasp is more characteristic of Him than existence, since existence, in the absolute sense, cannot be predicated of that which shall come to an end, or of that which has had a beginning, and He who now joins continuity of being with the possession of perfect felicity could not in the past, nor can in the future, be non-existent; for whatsoever is Divine can neither be originated nor destroyed. Wherefore, since God's eternity is inseparable from Himself, it was worthy of Him to reveal this one thing, that He is, as the assurance of His absolute eternity.

As far then as we can reach, "He who is" and "God" are the special names of his essence; and of these especially "He who is," not only because when he spoke to Moses in the mount, and Moses asked what his name was, this was what he called himself, bidding him say to the people, "I am has sent me," but also because we find that this name is the more strictly appropriate. For the name theos ["God"], even if, as those who are skillful in these matters say, it were derived from theein ["to run"] or from aithein ["to blaze"], from continual motion, and because he consumes evil conditions of things (from which fact he is also called a consuming fire) would still be one of the relative names and not an absolute one, as again is the case with "Lord," which also is called a name of God. "I am the Lord your God," he says, "that is my name;" and "The Lord is his name." But we are inquiring into a nature whose being is absolute and not [into being] bound up with something else. But being is in its proper sense peculiar to God and belongs to him entirely, and it is not limited or cut short by any before or after, for indeed in him there is no past or future.

So in Genesis [sic] he bade Moses say of himself, "Go and say to the children of Israel, I am who I am. He who is has sent me to you." So he wanted his eternity to be denoted by the present tense. This use …

The phrase "I am" belongs to the divinity. It does not change with time but is always there and remains eternal. So the reply to Moses was "I am who I am" and again "He who is has sent me." But we must first investigate …

Hold most firmly and never doubt that the holy Trinity, the only true God, just as it is eternal, is likewise the only one by nature unchangeable. He indicates this when he says to his servant Moses, "I am which I am."

Wouldest thou learn also His eternity? Hear what Moses saith concerning the Father. When he asked what he was commanded to answer should the Jews enquire of him, "Who it was that had sent him," he heard these words: "Say, I AM hath sent me." Now the expression "I AM," is significative of Being ever, and Being without beginning, of Being really and absolutely.

Perhaps it was hard even for Moses himself, as it is much also for us, and much more for us, to understand what was said, "I am who I am" and "He who is has sent me to you." And if by chance Moses understood, when would they to whom he was being sent understand? Therefore the Lord put aside what man could not grasp and added what he could grasp. For he added and said, "I am the God of Abraham, and the God of Isaac and the God of Jacob." This you can grasp. But what mind can grasp, "I am who I am"?

The Lord said, I am that I am, thou shalt say, I AM hath sent me unto you. This is the true Name of God -- Eternity.

You know to whom the first noble knowledge of the commandments was given? Certainly to Moses, who wrote through the Holy Spirit. But when did he have this knowledge? Certainly, when the Lord appeared to him. And in what manner did He appear to him? …

As related to pre-existent truth, in three ways: as regards essence, as regards excellence, or as regards refulgence. The divine essence is the first thing that comes to the mind. When Moses inquired about God's name, he was told: "I am who am," that is, …

The first object of speculation is the fact that God is. The first name of God is "To Be" which is most manifest and most perfect — and therefore, first. Hence nothing is more manifest, for anything said of God is retraced to being: this …

Now this is the most manifest and perfect name of God, for all things depending upon God are comprised within this name: "I am who am." This name is properly His, and it was said of it in what manner all things represent Him by …

The first mode first and principally fixes its gaze upon being itself, saying that He Who Is is the primary name of God. The second mode fixes its gaze upon the good itself, saying that this is the primary name of God. The first pertains …

As there is one Beginning and therefore one God, so one is that Essence and Subsistence which indeed and truly and really is. It is this One who said "I am that I am," and not two, that there be not two Beginnings; and from …

And God said unto Moses, I am that I am,.... This signifies the real being of God, his self-existence, and that he is the Being of beings; as also it denotes his eternity and immutability, and his constancy and faithfulness in fulfilling his promises, for it includes all time, past, present, and to come; and the sense is, not only I am what I am at present, but I am what I have been, and I am what I shall be, and shall be what I am.

Let it suffice us to know that he is what he is, what he ever was, and ever will be. How little a portion is heard of him! (4.) That he is faithful and true to all his promises, unchangeable in his word as well as in his nature, and not a man that he should lie.

I am that I am - אהיה אשר אהיה Eheyeh asher Eheyeh. These words have been variously understood. The Vulgate translates Ego Sum Qui Sum, I am who am. The Septuagint, Εγω ειμι ὁ Ων, I am he who exists. The Syriac, the Persic, and the Chaldee preserve the original words without any gloss. The Arabic paraphrases them, The Eternal, who passes not away; which is the same interpretation given by Abul Farajius, who also preserves the original words, and gives the above as their interpretation.

But he evinced great reluctance to it and stated a variety of objections [Ex 3:11, 13; 4:1, 10] all of which were successfully met and removed--and the happy issue of his labors was minutely described.

I am that I am - That is, “I am what I am.” The words express absolute, and therefore unchanging and eternal Being. The name, which Moses was thus commissioned to use, was at once new and old; old in its connection with previous revelations; new in its full interpretation, and in its bearing upon the covenant of which Moses was the destined mediator.

Your I am only exists because of His I Am. And as you exist from Him, so it is only from Him that you can find the reason and purpose of your existence.