The Doctrine of the Trinity

The doctrine of the Trinity, in and of itself, is evidence (not proof) of the existence of God. No one would have made it up. Are we accepting the explanation that ideas of gradual development of the concept from the life of Jesus recorded in Scripture, percolating through a widely disparate but semi-organised part of Mediterranean culture for three centuries account for the doctrine being accepted by the church as a whole?  If not, what other explanation do we prefer? When confronted with such puzzles, the Hindus and other polytheistic cultures just kept inviting in more gods. Ancestor worship merged with most other religious arrangements, as this reinforced the existence of the tribe and the importance of it. You might get a father-son god from that, but it's hard to figure out where a Holy Spirit would come from. The Zoroastrians (were there other dualists?) pictured two opposed gods. That doesn't look like it would grow into three interconnected gods in any way. I suppose a Hegelian thesis-antithesis-synthesis concept might come in that way, but if anything synthesis is farther from being a personality, not nearer.

Whenever we encounter some paradox or the impossible, rather than merely rejecting it we have to consider what the other choices must be and choose what looks most likely.  As with whether light is a wave or a particle, embracing the paradox is often the only way forward.