The Christology and Trinitarian disputes of the early Christian Church came from the clash of two irreconcilable desires of early church intellectuals, the theologians, who had been trained in pagan (Greek and Roman) metaphysical philosophy.
First, they wanted to be able to state that there was one God - because they had a prior commitment to philosophical arguments that led to the inference of one God as the basis of unity and coherence in reality; and secondly, they wanted to be able to state that Jesus was God.
Jesus was God, so there were at least two gods; but there could only be one God - for philosophical reasons, based on pre-Christian assumptions.
In simple logic, one of these two sides ought to give-way - and for a Christian the obvious side that needed to give way was that there was only one god. Christ implies polytheism. But for a convinced Classical philosopher, this could not be true...
This is the Christian dilemma.
In other words, Christians actually are, and ought to be, regarded as poly-theists - as Jews and Muslims have always correctly asserted! Christian polytheism was the position reached by Mormonism some 1800 years later.
Mormon theology is simple, clear, coherent, and honest (and beautiful) - and it is Christian: Christ-centred and based on the divinity of Christ.
Thus, Mormons (eventually...) solved the Christian dilemma by holding-fast to the divinity of Christ, and chucking-out monotheism.
In doing so, the Mormon prophet Joseph Smith created the first explicitly pluralistic metaphysical philosophy - a couple of generations before it was set down academically by his fellow American William James.
But the early Christian intellectuals were, apparently, as much psychologically-wedded to the truth of philosophical monotheism as they were committed to belief in the divinity of Christ. They demanded to fit the divinity of Christ into the pre-existing pagan philosophical scheme. Yet this cannot be made to make sense...
So these early theologians eventually devised a none-sensical mish-mash of words, to assert that there was only one God and that Jesus was God.
Both-together and ignoring-contradictions.
In such wise they 'solved' the Christian dilemma by denying that there was a contradiction. The dilemma was 'solved' by (complexly, not simply) denying there ever had been a dilemma...
They devised a 'mantra' - a form of words (the Athanasian Creed), and then insisted that all Christians would assert this form-of-words (or, later and elsewhere, something analogous) as the core truth of the faith. To the extent that many/ most Christians describe themselves primarily as Trinitarians!
The mantra was strictly nonsense; but the nonsense was relabelled mystery, or a higher truth beyond common sense and logic - and that has been the situation in mainstream Christianity ever since.
Well this is what happened - but did it work?
It 'worked' within the Christian churchs, mostly; by sociologically-solving the particularly vicious Christological disputes among the intellectual leadership within the Christian churches. Those who remained, agreed-to-agree on the validity of the mantra.
But what of the wider world? Did the Trinitarian mantra convince ordinary people, non-intellectuals, those without a stake in the hierarchy? If Mormons eventually took the simple-coherent polytheist-path to solve the Christian dilemma; what about the the simple-coherent monotheist path? Did anybody reject the Trinitarian mantra and take the monotheist path?
Well, it seems that nobody knows the exact historical details - but my assumption is that Islam was the actual monotheist solution to the problem of the Christian dilemma. In Islam the oneness of God was retained, at the cost of the divinity of Christ; who instead became regarded as a great prophet.
Simple, clear, coherent, and honest.
But, obviously, not Christian.
The rapid and permanent rise of Islam seems to show the deep and intractable failure of the Trinitarian mantra - and how vital it is that the basic explanation at the core of a religion makes straightforward common-sense.
There is no more powerful a critique against the fundamental error in building Christianity on meaningless metaphysics and evasive theology than the rise and success of Islam. Islam is the failure of the Trinitarian mantra: Islam is the consequence of trying to evade the Christian dilemma.
The above analysis is one (but not the only) reason why I am a believer in Mormon Christian metaphysics and theology.