yeah, but we are not looking at this in terms of grammar, but theology.
I don't see how you can insulate theology from grammar when the basis of your theology here is grammatical consistency.
God IS not flesh because He IS an eternal communion of Three Persons. God is not a "What" but rather a "Who."
This, for instance, is a purely grammatical distinction. Not an actual one. There is no actual difference between man as a "what" and man as a "who" unless "man" is used to refer to men collectively. As the Fathers say, the difference between essence and hypostasis is only the difference between general and particular.
flesh, is not the "Who" when it comes to Christ, so it would be improper I think to say God is flesh, no matter what proper grammar would say.
"What" is a part of "who". "Who" is not distinct from "what". That's why "God" can be used to mean a nature or essence (species), but can also be used to refer to an individual specimen (hypostasiss) of that nature. As can the term "man". According to John of Damascus, the composite hypostasis of Christ "carries, according to the flesh, particular and distinctive characteristics distinguishing it from its mother and all other human beings". To distinguish these characteristics from flesh can only be done abstractly, not actually. He further says, "We also confess the single incarnate nature of the God-Word, because we say incarnate, and proclaim in this way the essence of the flesh." (This is, of course, how Severus meant it, but as per Meyendorff, Saint John of Damascus incorrectly believed Severus was a Eutychian, just as Severus incorrectly believed Chalcedon was Nestorian). The Word, in joining flesh to Himself, in cloaking Himself in it, did not keep it "external", but
enhypostasized it. That is, the very Word was made flesh (since it would be improper to say flesh was made the Word, as Christ's flesh never existed in itself, but only as part of the Word). The Word's divinity and the Word's humanity are actually and functionally
one nature, but are called
abstractly, mentally, verbally,
grammatically "two" purely for the purpose of preserving the doctrine of the
integrity of both, in contrast with Eutychianism.
I agree, I just said that above. I don't get how you conclude that everyone would have given the Sermon on the Mount if not, but whatevs.
Because in Gregory of Nyssa's letter to Ablalius, the whole reason we don't refer to God's three hypostases as three Gods, whereas we refer to three human hypostases as three men, is because God's hypostases have a common energies, whereas human energies vary according to hypostasis. If humans shared one energy, they would have the same unity of action as the Trinity; no single hypostasis accomplished creation without the other two, or freed the Jews from Egypt, rather they did as one because their energies are common and one; though the Trinity is existentially three, He functions as One God, HE IS.