First, on how we should be disposed to see the doctrine in relation to Scripture:
It is better to speak of the testimony of the Scriptures than to say that the existence of the Trinity is proved from the Scriptures, for the Trinity is not proved, nor is it a theological conclusion, but it is believed. To say that it is proved from the Scriptures is to insinuate that faith is the conclusion of this syllogism: Whatever God has revealed is true and is to be believed. But in the Scriptures God had revealed the mystery of the Trinity. Therefore I believe this mystery. The real conclusion of this syllogism, however, is that the Trinity is believable and should be believed. This is a judgment of credibility, but not an act of faith which is simply an essentially supernatural act, above discursive reasoning, and never the result of a syllogism, because it is based immediately on the authority of God the revealer, inasmuch as I believe in God revealing and God revealed by one and the same act
Next, on the progressive grades of argumentation that one goes through in discussing the Trinity:
Some students have tried to see in these treatises an illative process where there is only an explicative process which is merely the progressive understanding of one and the same revealed truth.
Both quotations- though especially the middle section of the first- might not merit scrutiny to the letter, but the general points are strong and salutary. Both resist the idea that the Trinity is a conclusion from prior premises: that the doctrine arises out of simpler and more basic truths. At the basis of our belief we do not find a series of premises, but an authority commanding assent. The question is not so much which premises to start with but what the organs of authoritative revelation are. Scripture enters both as an authority (though GL does not stress this) and as giving testimony to the authority.
Our problem is discussing the Trinity is, to a large extent, the scandal of authority. Everyone wants to be his own theological authority just as much as every child wants to be his own authority on when his bedtime should be, what he should get to eat, and how much TV he should watch. Everyone would rather be the one in charge. Contemporary persons have a uniquely difficult problem with authority since the whole structure of our intellectual system rejects the idea that there should be an authority binding the intellect on questions of the faith. Political correctness is an assertion of just such a binding authority upon the intellect- and the authority that is exercised here is not bad in itself, even if one claims it is mistakenly applied- but PC does not apply to questions of the faith, which are assumed to fall under the umbrella of an absolute academic freedom.
While every man in every age will chafe against the reality that he is not the authority deciding a theological question, and that what he can think is bound by the authority of another, we contemporary persons have an additional social and institutional difficulty with intellectually binding faith authority. It is assumed that the domain of academic discourse on the faith is one where there is not and should not be an authoritative voice. We have the right to think and say whatever we want- and this is how it should be. Even the decision to follow an authority is seen as just another choice in a world where anything goes. At the very least, it is not evident that this is the healthiest atmosphere to discuss the faith.
To be clear, I’m not saying that I would prefer that academic culture were different. I am habituated to it, and it’s not clear to me that another one is entirely possible or would be on the whole desirable. But working within ones culture requires knowing its limitations, and our reaction to authority in matters of faith is one of those limitations.
Just Thomism 