??? Um, well, actually, the majority who eventually won the fight would strongly disagree that a belief in Trinitarianism (capital T) isn’t necessary to be counted among the majority who eventually won the fight. That’s why there are Nicean and Chalcedonian creedal statements (with a variation of the latter being the two main parts of the so-called Athanasian Creed).
However, that’s after the fighting, which started late 2nd century but didn’t get particularly systematic until the 4th century. Before then (and during the original disputes leading up to the 4th century), things are a lot looser in some ways, just as strict in others. But I think it’s important to understand that the technicalities which came later followed from trying to figure out how best to affirm and not deny the stricter portions of the looser earlier time. The quote from Origen upthread illustrates that principle. He wants to protect the affirmations of the faithful deposit, and is prepared to get more technical than people generally were previously, in order to do so; but he won’t be as technical as the people who follow after him – largely following his leads and methodologies! Both of which are directly connected to Patristic arguments for Christian universalism, by the way.
(I will briefly mention here, in regard to another thread on a similar topic, that no one thinks Athanasius was a ‘unitarian’, and he was explicitly following Origen’s lead in his disputes with Arius. While he thought he had to defend Origen sometimes, because O hadn’t gone into quite the detail they were having to go into a generation or two later, Ath studied under disciples of O and had vastly much more access to his original work than anyone living today. From that alone I would find it almost impossible for anyone, arguing from scattered surviving remnants of Origen’s work, to convince me that Origen was a unitarian. Be that as it may. )
What does little-t (as you put it) involve? The dispute was then, and has always been, centered on this: who should we be (and not be) religiously worshiping, and why? Little-t says there is one and only one God Most High, and we should be religiously worshiping only God Most High not any lesser lord or god, and also that we should be religiously worshiping the Father, the Holy Spirit, and the Son Who was born of a woman as Jesus of Nazareth, who are three distinct persons not (merely) roles of the same person in relation to us.
Why did little-t go that way? Because that’s what they heard their teachers saying, and that’s what they found being said and taught (and claimed by Jesus) in the oldest texts with the widest use across the world where people religiously affiliated with Jesus somehow (though those texts are a little fuzzy in some ways about whether the spirit is a distinct person compared to the blatantly obvious personal distinction between Father and/or the Son).
Big-T says the same things, just in more technical details. But the technical details arose because of practical questions about whether little-t really had the basic data right to begin with, which was important partly for purposes of being faithful to the original teachers (going back to Jesus) and partly for purposes of worshiping and evangelizing properly (rightly praising and rightly teaching others about God – both of which are what ortho-doxy, right-representation, can mean.)
That’s why even among the Big Three Big T groups (insert topical irony here as appropriate ), they started ostracizing and badmouthing one another eventually, actually creating the distinctions of those groups while doing so, where no such hard distinctions previously existed: the Oriental Orthodox (connected to Alexandria), the Church of the East (connected to Antioch), and the Catholic Orthodox (in the middle, touching Rome and New Rome). They weren’t just being naturally ornery (although there was some of that, too) or politically motivated in the patronage system of the ancient world (although ditto). The question of how the two-natures of Christ (which all three sides agreed about) relate to one another, and to us, touches the question of what was and wasn’t accomplished for us in Christ, and touches the question of whether we really ought to be worshiping Jesus himself personally (though all three sides agreed on that, too).
Is that really necessary for Christians to get into today? From a practical perspective, probably not, as long as they believe little-t has the basic data right and are willing to act religiously on that without being worried about further details. But then, little-t has what looks like a major conceptual contradiction in its set: religiously worship only the one and only God, and religiously worship the Father, the Son and Holy Spirit. What is religiously idolatry, and what isn’t? Maybe that wouldn’t be so much of a practical problem if the scriptures didn’t indicate God cares a lot about idolatry, but they REALLY REALLY REALLY REALLY DO (OT and the new texts both).
So there are huge tensions. Leading to a huge T out of the little t.
(Then Islam comes along and provides a theologically simpler set of data by replacing the old data sets altogether.)
I’m pretty sure they proclaim against the little-t set, too; the little-t set just avoids the questions by focusing on the practical aspect of worshiping only God most high and worshiping F/S/HS. As long as people are doing that, what’s the problem, right? It’s an inscrutable mystery but if the authoritative texts point that way then why worry about it?
See, the inscrutable mystery parachute doesn’t start with Big-T. Big-T imports it as a problem solving tactic from little-t; but whereas Big-T is Big-T by also trying to meet and solve problems in other ways, that appeal to revealed mystery data is all little-t is in a position to do.
But I’ll have to illustrate that later; off to home now.