I posted this as a response, but I'll put it out as a general comment.
God, in the Old Testament, went out of His way to declare, explicitly and repeatedly, that he alone was God. The Jews got the message loud and clear, to the point monotheism became THE defining theology if the nation. God's singleness of person wasn't something inferred from single pronouns, God went out of His way to push the nation that direction in their understanding.
It bothers me when "modern Hebrew scholars" look at the writings of the OT and claim to see multiple personal subsistences. I understand English better than a non-native speaker because I've been immersed in it, with all of its nuances and cultural subtleties, from birth. For someone to come along 2,000 years later and claim to find something that the real Hebrew scholars would have died to disprove is preposterous. All native Hebrew scholars agreed, God had one mind, consciousness, etc.
Another thing that disproves a Trinitarian understanding of the OT is the fact that God, knowing the Jews believed in one divine person, went out of His way to say "I created things by myself - there is none like me, with me, beside me, before me, after me, etc". If God knew that they were misunderstanding His nature, it is not His M.O. to push them over the edge and deeper into hard-core deception.
Both the Shema and the first commandment were engineered specifically by God to convey absolute singularity of will, person, center of consciousness, etc. The first commandment, which the NT attributes to The Father, says (paraphrased) "in your theology don't put any second person (literally) beside me, with me, or before my face"
It is far more likely that God, knowing He Himself was going to come in the flesh, and knowing it could get confusing, wanted to first leave no doubt when Jesus came that it was The Father in flesh. When someone came that was called God, he wanted no doubt that it was Him.
Again I reiterate the fact that Hebrews says the one speaking through the prophets is the one who has a son (only the Father can be referenced here).
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