I believe it was for so years ago when I read R.G. Collingwood writing that the doctrine of the Trinity was a brilliant solution to the problem that had plagued ancient metaphysics. I am beginning to get the hang of what he was talking about.
Different strands of ancient thought had stressed different aspects of reality: the Platonists had stressed ideas, Aristotle and his followers the realized expressions of the ideas, the mystery religions the experience produced by the first two.
Which ever of the above was stressed, the other two aspects of reality tended to be neglected, at least to an extent. It was as though the ancients had a hold of a three-legged stool but everyone was trying to sit on it with only one leg on the ground.
The doctrine of the Trinity placed all three legs on terra firma. The idea (the Father), its realization (the Son), and the experience that "proceedeth" from the idea and its realization (the Holy Spirit) are separate but equal persons, all "one in being."