A good book on the origins of Western civilization, aka, Christianity, is The Five Stages of Greek Religion, By Gilbert Murray.

https://www.gutenberg.org/files/30250/30250-h/30250-h.htm

His general point is that Christianity arose as a marriage between classic pantheism and Jewish monotheism.

The Trinity came from the Greek year gods. The son reborn in the spring of the sky god and earth mother.

Basically Gnostic Christianity was an attempt to re-invigorate institutions that had grown stale and formulaic over the centuries, with the vision of Jesus reborn as a fitting metaphor.

The problem with the premise of monotheism is that a spiritual absolute would necessarily be the essence of sentience, from which we rise, not an ideal of wisdom and judgement, from which we fell.

As the absolute is elemental, while the ideal is aspirational, the practical effect of multiple competing monolithic theologies is polytheism.

To the Ancients, gods were not so much metaphysically anthropomorphic, as they were the ideas, ideals and memes animating the world.

So in their worldview, monotheism equated with monoculture, as in one people, one rule, one god.

Remember that democracy and republicanism originated in pantheistic cultures, as that was more metaphorically representative of multiculturalism. The many networking and interacting.

The Romans co-opted Gnostic Christianity, as the Catholic Church, as the Empire solidified and remnants of the Republic were being erased.

Given there was little distinction between culture and civics, this served to validate top down authority and consequently the default political model for Europe, for the next 14-1500 hundred years, was monarchy and feudalism.

When the West went back to less centralized political systems, it required the separation of church and state, culture and civics.

Of note, Islam was not adopted by an existing political system, but arose on the fringes of that Empire, by those who saw the power of a common creed. So the relationship between religion and state is reversed.

Personally my own version of the Trinity is the absolute, the extant and the infinite. Once I tried arguing that with a Catholic priest and future in-law, who was quizing my beliefs. His response was to cross himself and walk away.

Past, present and future is a close approximation though. Potential, actual, residual.