Hector is, as far as I understand, an Anglican Christian who embraces most Roman Catholic liturgy, and his ethnicity is Indian, as in, the Indian subcontinent, not Native American. He has recently posted at Alexandria a long piece on The Trinity and the terrible heresy of "modalism," a heresy of which he has accused me in the past. I cannot respond to him there, being at present banished from the pond by the Ruler of All He Surveys whose divine majesty I offended some months ago. So I will do so here - albeit this may be a little confusing for anyone else trying to follow the debate.
I should note, when I say that Hector "accused" me, that this was done in a friendly and mutually respectful manner. Hector takes doctrine seriously, although by some lights he is a bit unorthodox. For instance, he's not at all sure that homosexuality is a sin. Hector and I generally agree on economic issues. We both favor some sort of socialist policies which more equably divide the fruits of labor among ALL who produce it, without, I think, violating the principle that "those who work will eat," provided an opportunity to labor is indeed available to everyone.
Hector is deeply devoted to the Trinity. I am at best indifferent to it. If it brings you closer to God to think of God as a Trinity, I am not so militant a lower-case unitarian that I need to argue you out of it. Ultimately, God is a mystery, and must be taken on faith, so anyone who wants to be purely rational about it can easily argue their way to atheism.
Hector has now argued that the concept of God as Trinity "is a persistent and permanent affront with those rationalists who would do away with mystery, with miracle, and with the supernatural." I see this entire question from the opposite end of the same telescope. Insistence that the Trinity IS an accurate and essential understanding of what God IS, rests on a kind of rationalism, which is an affront to the ultimate mystery of God.
Yes, the notion that God is one divine essence in three divine persons does defy rational thought, so much so that it easily leads the unwary into tritheism, which Hector explicitly rejects. Whenever anyone tries to defend the Trinity in a rational or logical argument, they always end up invoking the explanation, "It's a mystery." My point is simply, since it IS a mystery, why pretend that we know the answer? Just leave it at that: what is the nature of God? It's a mystery. Period.
Indeed "human reason was not designed, nor is it capable, of comprehending the essence of the Trinity. We cannot understand it." But that being the case, and there being no divine revelation to guide us, why should we "acknowledge it." What does it add or detract from our sense of what God requires of us? (One verse of Micah, and three in the Gospels, suffices to tell us what God requires of us. Hmmm... one and three. If I were into numerology, I would concede the argument, but I'm not.)
I have been known to suggest that the Trinity is like three blind men feeling an elephant: some feel a trunk, some feel a leg, some feel a flank, and all believe they know the essence of what the elephant IS. They are all part right, and terribly wrong. But if they put these three perceptions together, without recognizing that these are simply appendages, if they said the elephant is a symbiosis of three different persons, they would also be wrong. Hector calls this "Modalism."
I won't repeat at length what Hector says about the error of "Modalism." It is all available at the link provided in the first paragraph. Hector sees Modalism "as a knife pointed at the heart of the Christian Faith, for if Modalism is true, then Christianity is a farce and a lie, and Christ was simply a sham, a cosmic joker."
I can't imagine why. If God really doesn't have three persons, Christianity is a farce and a lie? How so? The shock and horror have leapt far ahead of any logical progression from premise to conclusion. True, logic is a poor foundation for faith, which is why I hardly see that such doctrines matter in the slightest.
"You can see right away why this doctrine is so appealing to the modern West. It fits perfectly with the gospel of postmodernism, by which perception is reality, and by which each person’s worldview and opinion is equally valid." Hmmmm... I place little stock in postmodernism, especially since "modern" is itself a relative notion. In every generation people have announced that "modern times have arrived," and every decade or two, a new modern takes the stage. I am perfectly certain that there is an absolute Truth to the universe in which I live, and that it is what it is, regardless of what I think of it.
I have pointed out many times that the first two clauses of the First Amendment to the Constitution of the United States of America neither establish nor imply that all worldviews and opinions are equally valid. The First Amendment proceeds from the understanding that the instruments of human governance are incompetent to declare which, if any, religion is the True Faith, and all humans must be free to pursue this truth for themselves as best they can, without interference by the blunt instrument of the law.
But what does the Trinity have to do with any of this? If God is One and not Three, then there is no absolute truth to Creation? How in the Name of God does THAT follow? The supposed horror is offered to spice up the argument, without ever establishing causality.
I would certainly agree that the "prospect of Jews, Muslims and Christians coming together and sharing a common understanding of God, is very appealing." I adhere to the statement by El-Hajj Malik el-Shabbaz, upon return from Mecca with that name (he was previously known as Malcolm X), "The God we worship is the one who created the universe. Isn't that the same God you worship?" Of course it is. And THAT is what is important. The shape of that God, the nature of that God, which are indeed unknowable to us, is of no particular importance. It could even be described as hubris to attempt to write doctrines on the subject.
Beyond that, for now, I will say only that many paragraphs of the essay I linked to above, and have responded to here, are pure tautology. IF God is a Trinity, then it is an insult to his divine majesty to deny it. The premise is the preordained conclusion, which logically proves that if A is true then A is true, without ever establishing anything else, or indeed, any foundation for the truth of A. That is the nature of all defence of the Trinity, passionate or logical.
The bottom line is, "De Trinitate" advocates belief in the doctrine that God is a Trinity, because it would make God a better god, or because it would help to undermine the appeal of secular Western culture, or for any reason except, because it is true. There being little evidence, or possibility of evidence, as to the truth or falsehood of the doctrine, it becomes a matter of conjecture and personal preference what to believe. Does it really matter to God how well we understand the details of what we are incapable of knowing?