One Essence Three Persons of Trinity

Question

I thought that the trinity came from the following revelations
(1) There is one God (I myself am He! There is no god besides me.) (2) The Father is God (3) Jesus is God
(4) The Holy Spirit is God
(5) The Father is not the Son, the Son is not the Holy spirit, the Holy spirit is not the father.

I found the usual expression of the trinity in orthodox Christianity is "One Essence Three Persons". I think I understood why there is "Three Persons" but I don't understand why there is "One Essence". At a glance I thought it stands for There is one God. But the word Essence means different thing from "I myself am He! There is no god besides me". While the old testament revelation means one(singular) personal(I, me) God the "One Essence" means a very abstract "being" which can't be one person.

So my question is: where can I find One God by (1) above in the Trinity expression "One Essence Three Persons"? Can I assume "One Essence" means One God which is represented by I and me? Does "One Essence" mean monotheism in the sense of (1)? But I doubt it from the very meaning of Essence which I think is very foreign in the Bible.

Sorry, let me clarify my question in the followings.

Who is "I" and "me" in (1)? Is it the Father or the Son or the Holy Spirit or God as One Essence?

If it is one of the Father, the Son, and the Holy Spirit then how he can say "there is no god besides me?" So I want to have one God who can say that. And I am tempted to see One Essence as the one God. But I don't know if it makes sense or not since Essence is about "what" not "who" as you explained.

Answer 1

The relationship of the Persons (Greek hypostases) of the Trinity to their Essense (ousia) is addressed by Protopresbyter Michael Pomazanski in his Orthodox Dogmatic Theology as follows (in abridged form):

The Three Hypostases of the Holy Trinity have one and the same Essence; each of the Hypostases has the fullness of Divinity unharmed and immeasurable; the Three Hypostases are equal in honor and worship.

In the history of the Church, the chief dogmatic work of the Holy Fathers was directed towards affirming the truth of the Oneness of Essence, the fullness of Divinity, and the equality of honor of the Second and Third Hypostases of the Holy Trinity.

In earliest Christian times, until the Church’s faith in the Oneness of Essence and the equality of the Persons of the Holy Trinity had been precisely formulated in strictly defined terminology, it happened that even those Church writers who were careful to be in agreement with the universal consciousness of the Church and had no intention to violate it with any personal views of their own, sometimes, together with clear Orthodox thoughts, used expressions concerning the Divinity of the Persons of the Holy Trinity which were not entirely precise and did not clearly affirm the equality of the Persons.

This can be explained, for the most part, by the fact that in one and the same term some shepherds of the Church placed one meaning and others placed another meaning. The concept of “essence” was expressed in the Greek language by the word ousia, and this word was in general understood by everyone in the same way. Using the word ousia, the Holy Fathers referred it to the concept of “Person.” But a lack of clarity was introduced by the use of another word, “Hypostasis.” Some signified by this term the “Persons” of the Holy Trinity, and others the “Essence.” This circumstance hindered mutual understanding.

Finally, following the authoritative example of St. Basil the Great, it became accepted to understand by the word Hypostasis the Personal attributes in the Triune Divinity.

He elaborates specifically on how the Persons and the Essence of God relate to one another through the example of Christ:

(a) The Lord Jesus Christ is not only God, but also became Man, and such expressions can be referred to His humanity; (b) that in addition, He, as our Redeemer, during the days of His earthly life was in a condition of voluntary belittlement: He humbled Himself, and became obedient unto death (Phil. 2: 7– 8). In keeping with these words of the Apostle, the Fathers of the Church express this condition by the words ekkenosis, kenosis, which mean a pouring out, a lessening, a belittlement. “Foreseeing Thy Divine self-emptying upon the Cross, Habakkuk cried out marveling” (Canon for the Matins of Great Saturday). Even when the Lord speaks of His own Divinity, He, being sent by the Father and having come to fulfill upon the earth the will of the Father, places Himself in obedience to the Father, being One in Essence and equal in honor with Him as the Son, giving us an example of obedience. This relationship of submission refers not to the Essence (ousia) of the Divinity, but to the activity of the Persons in the world: the Father is He Who sends; the Son is He Who is sent. This is the obedience of love.

Answer 2

The O.P. correctly affirms the following, which can be attested by the Scriptures:

(1) There is one God (I myself am He! There is no god besides me.) (2) Jesus is God (3) The Holy Spirit is God (4) The Father is not the Son, the Son is not the Holy Spirit, the Holy Spirit is not the Father.

I would add, between (1) and (2) “The Father is God.” There is, moreover, quite a bit more that we can gather from the Gospels: for example, the Son is sent by the Father (John 20:21); the Holy Spirit proceeds from the Father and is sent by the Son (John 15:26); and so on.

The terms essence (Greek: ousia) and person (Greek: hypostasis) are simply ways of expressing what the O.P. has stated in more technical, philosophical language.

The simplest way of looking at it is as follows: ousía means (according to Aristotle’s famous definition) “what a thing is simply because it is” (in Greek: to ti en einai; this is explained in Metaphysics VII). In other words, ousia answers the question “What is it?” (Greek: ti estí? which becomes Aristotle’s most common synonym for ousia).

So, in answer to the question, “What kind of being is the Father?” the answer is “God;” and the same can be said for the Son and the Spirit. Using the technical language adopted by the Fathers, we say that Father, Son, and Holy Spirit are the same Essence (ousia); that is—to use the term actually found in the Nicene Creed-they are homoousios or consubstantial. (Note that the Greek term ousia can be translated both essence and substace; the ancient philosophers made no distinction between the two.)

On the other hand, person (hypostasis) in Trinitarian theology and Christology always answers the question Who? For example, “Who became incarnate?” Answer: “God the Son alone.”

Although the terms ousia (essence) and hypostasis (person) are not employed by the New Testament writers to speak about the Trinity explicitly, that forumlation faithfully expresses what is revealed in the Scriptures.