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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.