"Much Christianity for all practical purposes is a kind of tripartite polytheism"
Tripartite yes, but I'm not quite so sure about the 'polytheism' element...at least in my investigation.
My analysis has lead me to conclude that a monotheistic evolution of traditional Judaism into a Platonic Hellenic Judaism has taken place, where Jehovah is replicated and then escalated to emulate the captain of Plato's 'Just Soul'.
The 'form' of Justice as you know is particularly outlined in Plato's Republic and is composed (or the father of) of 3 elements, mind, spirit/courage and appetite which all work in concordance with one another.
Plato considers a person perfectly 'just' when these 3 elements are working in harmony, the mind being chief.
Plato then goes on to parallel this 'just soul' to that of a 'just city' which is comprised of Philosopher Kings, Military and Citizens.
You might see where I'm going with this.
"Now when He was asked by the Pharisees when the kingdom of God would come, He answered them and said, "The kingdom of God does not come with observation; nor will they say, 'See here!' or 'See there!' For indeed, the kingdom of God is within you."
"While he was sitting on the judgment seat, his wife sent to him, saying, "Have nothing to do with that just Man, for I have suffered many things today in a dream because of Him.".......When Pilate saw that he could not prevail at all, but rather that a tumult was rising, he took water and washed his hands before the multitude, saying, "I am innocent of the blood of this just Person."
The Christian 'Kingdom of God' is Plato's Polis and Plato was the first to articulate 'The Kingdom of God is within you' by paralleling the Polis to the Soul.
The soul and the city are comprised of 3 elements which is held together by the virtue of Justice. Jesus (as an everyman figure) was a manifestion of Gods Kingdom on Earth who's mind, spirit and appetite were concordant with the will of God (Justice).
KINGDOM OF GOD:
2) Holy Spirit
CITY OF PLATO:
SOUL OF PLATO:
Paul was a product of middle Platonism an synthesized Plato's form of Justice into Abraham's righteousness.
Romans and Galatians are all about the Justice of God through Christ.