It sounds like your view might be that the Father and the Son are two distinct beings who are both everywhere?
One of the problems with this discussion is that you keep wanting to know about the terms "being" and "entity", but no one seems to know exactly what you mean by them, and thus we are not capable of answering the questions that involve them. If you want to keep using them, and really want an answer about them, I think it will be necessary to succinctly define them.
What is a subsistence? I thought subsist meant exist.
"Subsistence" is really the best translation of the Greek "hypostasis" I have come by so far. Yes, it means something close to "existence". More exactly, however, it means the individual existence of a particular substance/nature. This means that the Father, the Son, and the Holy Spirit are of the same existence, but they are three individual instances of it.
What is a hypostasis?
Beginning in the mid 4th century and since then, hypostasis has been used to essentially mean the individuated existence of a class of being.
What substance is God?
The substance of God could perhaps be called "divinity".
And in what way are they “one” in substance?
Like I said, everything that the Father is the Son also is, save that they have come into being in different manners. The Father has no origin and the Son is begotten from the Father. That everything the Father is the Son also is, save that they are two different instances of this one "isness", is what it means for them to one in substance.
If the Father was literally present in Jesus, why did Jesus say his Father was in heaven and had sent him from heaven to earth,
Because He condescended to take as His own an instance of humanity from Mary.
and that he was returning to heaven to be with his Father?
This is because His humanity was not yet in Heaven. He went to Heaven to be with His Father because He ascended in His circumscribed humanity.
Yes, I meant the Father. When I say God I generally mean the Father. Not that I object to calling Jesus God. I just think the Father is primarily called God.
Well, I can't fully answer your question yet because "being" has not yet been defined. I could answer it according to my understanding of the word, but that would be a hasty thing to do as you might not mean the same thing by it. However, given your clarification of what you mean by "God", Jesus was eternally begotten by God, and is in all things the same as Him with respect to divinity, save that He is another instance of the same divinity.
Ok, a divine hypostasis is everywhere therefore the multiple divine hypostases have “a oneness in existence.” I'm not sure what it means to be everywhere. If these divine hypostases were everywhere or immeasurably vast and were able to transcend each other, wouldn't they still be three distinct beings or entities?
How could things that were each everywhere with each other and each immeasurably vast in the same way be said to "transcend each other"?
I still don't understand what eternally begotten means. It makes me think of emanation. Is this “begetting” the primary reason Jesus is called God?
Yes, but not after the temporal manner of Man in which a child is one moment non-existent and the other moment conceived, but He is being begotten outside of time, such that the "this then that" form of human begetting cannot apply.
It sounds like you are saying time has boundaries. What does “not temporal” mean? That doesn't seem possible or coherent to me.
Time is segmented into various moments through which we pass. At one time we are in one moment. Then we leave that moment behind and enter into another; this process continuing over and over again. Eternity is not like that. It is not segmented and it is not made up of various moments or points of time that are each gradually passed through. It just is. God even points to this when he says "I Am Who I Am".
Basically. I meant “continually”. Eternally Begotten sounds exactly like Continually Begotten to me.
No, it means it is actually transcendent to the very process of passing from one moment to another.
That sounds, to me, like a unique way of saying “nonexistent”.
The Fathers have said that God is beyond existence, yes. However, regarding God as "non-existence" is to have a narrow minded view of reality by which temporality is the only dimension in which something can exist. The Christian Tradition has taught otherwise.
Temporal boundaries again. I'm really not sure that is a coherent concept. I'm not saying I disagree or intend to refute your beliefs. I just don't see how it can actually mean anything.
Well, it makes perfect sense to me. Something just being, not being here, then there, then the next place, or in one time, then another, then another.
In my understanding, there is no such thing as atemporality so everything God does must be in a different manner than what you call “eternal”. Is atemporality an official Orthodox Church doctrine? Is it necessary to hold to atemporality in order to say whether the Father and Jesus are the same being or not?
Well, I think you are in error in saying that there is no such thing as alternatives to temporality. That is essentially what "eternity" is understood to mean in our Tradition, as far as I understand. And yes, I think it is necessary to believe that in order to understand that the Father and Jesus are one God, because otherwise you get "there was a time when the Son was not", and the Son is rendered a creation.
You teach Jesus was in heaven at the same time he was on the earth?
Yes. Jesus was on Earth and in Heaven in His divinity and on Earth in His humanity.
Do you believe Jesus had a human soul and spirit?
The Church teaches that Jesus had limited and unlimited strength?
Jesus had the capacity for unlimited strength because He was divine. He was limited in His strength only when He deigned to operate in such a manner through His humanity.
Because God is impassible and immutable. He is always divine and cannot change into another thing. The only thing that can happen is a particular hypostasis takes on an instance of another class of being into Himself and subsist in it as His own without changing His divinity.
What does it mean that he “took on” a human body, soul, etc.?
It means that He came to possess and subsist in a human body and a human soul as we do.
You said he was in heaven and that his hypostasis was “everywhere”.
He is everywhere with respect to His divinity, including Heaven and Earth. He was on Earth with respect to His humanity. Then He ascended into Heaven with respect to His humanity. And then He came to present on Earth in a mystical manner in the Church through the indwelling of the Holy Spirit.
It sounds like he took control of a human body and soul while remaining immeasurably vast or everywhere.
No. He didn't possess a human. He became a human while remaining also God.