I’m an atheist, so take my opinion with a grain of salt, but I was also educated by jesuits and am well-read in the Bible, theology, and philosophy.

I’d say that if you assume God is a real thing, the trinity obviously seems like polytheism and makes no sense.

But… if you imagine that God is a metaphor for value (or what Pirsig called Quality), then it makes perfect sense to say that value can be experienced in three different modalities.

Theologians and philosophers call these modalities the “transcendentals”: beauty, goodness, and truth.

I prefer this view. From earliest animism, which basically just attributes agency to nature, you eventually get polytheism, which assigns a person to every value or every form of excellence.

Monotheism suggests that no, all our values and our sense of excellence is just different manifestations of one underlying sense of Value that imbues nature.

And then the trinity is a further refinement, saying that no, there may only be one ground of value, but we can only experience it in at minimum three different ways, corresponding to our sense of truth, of morality, and of aesthetic pleasure. The other values or excellences are derivative of these three.

You might find this article interesting:

https://medium.com/excommunications/the-real-meaning-of-the-holy-trinity-b875ab3a5fa1