Trinitarianism is neither Jewish nor Christian; it is polytheist. Certain factions approve this teaching because it permits them to demote Jesus, who, as a man, was God, with us, in Christian belief. Iow, he was the manifestation of God, in Christian belief.
Jesus himself isn’t and never was a part of the holy trinity, but was rather a blueprint for the Son - the Son being a man made perfect in love, in the image of the Father. Jesus was one example of a Son for the rest of us to follow, so to become Sons ourselves.
In truth, the Buddha was another blueprint of the Son, another example for us to follow, though most self-identified Christians would be appalled by the idea.
Buddhism is just the thing these days for claimants to Christianity. Real Christians will barely bat an eyelid unless someone attempts to interpret the Bible.
You’ll have to make sense of this yourself, think it through yourself. I can’t show you the truth, nor can anyone else - each of us must find truth by and for ourselves.
What I can do is leave you with a parallel example from the Eastern religions, particularly Hinduism: the Son is to the Father what the Self (Atman) is to Brahman.