The other reply offered a perfectly good set of corrections but I want to add my own clarifications.

One point I wanted to make in my original comment was that monotheism vs polytheism is not a helpful object category when talking about 2000 year old religions as their adherents understood it. This analytic category is a fairly recent invention. You can make this distinction if you want, but it will be of precious little use for actually understanding the people of the past.

It’s also not helpful to back-project contemporary understandings of Judaism back into the religious context of the 1st century. The idea that the messiah would be in some sense divine, or even that he would be YHWH Himself, is not purely an invention of the Christians, but was present in Jewish groups prior to Jesus. I would argue this has not even been entirely purged from all strands of modern Orthodox Judaism. This doesn’t even get into stuff like the Zohar/Jewish mysticism where you have 12+ special flavors of God.

All of these groups would have insisted that there’s one true God, but they would also have insisted that he had more than one hypostasis.” Romans at the time also believed that a single God could have different hypostases.* Nevertheless despite this agreement they accused the Christians not of being monotheists but of being atheists because the Christians alone refused to pay respect to any of the hypostases of any of the recognized gods.

The idea that Jesus is depicted as having some kind of separate agenda from His Father is also a very bizarre reading of the New Testament. Jesus’ relationship with The Father seems to be much more complex than that since he says The Son can do nothing Himself and that He only does what the Father is doing, that He and the Father are one, etc.

There nonetheless seems to be some kind of distinction between Them, hence the two thousand years of theological debate. If you want some sources on this type of thought prior to and parallel to Christianity, you can read the book Two Powers in Heaven.

> Writing Jesus into the canon 2000 years later as a seperate but equal entity was bound to be fraught with continuity issues.

If you pay any attention to Christian history, you would know that this goes back to the very founding instead.

> ... most of the new testament has him [Jesus] as a fully separate person with his own separate agenda ...

Just want to correct a couple errors of fact here, by quoting from the sources that you're misunderstanding.

"And he withdrew from them about a stone’s throw, and knelt down and prayed, saying, 'Father, if you are willing, remove this cup from me. Nevertheless, not my will, but yours, be done.'" - Luke 22:41-42 (copied from https://biblehub.com/esv/luke/22.htm)

He doesn't want to suffer and die on the cross. Yet he chooses to serve the Father's agenda, not his own.

"I and the Father are one." - John 10:30 (copied from https://biblehub.com/esv/john/10.htm)

And note that, if you read just a few more sentences, you discover that this statement caused the Jews listening to him to pick up stones to stone him (for anyone who doesn't know, stoning was a method of execution: they intended to kill him). He asks (verse 32) why they want to stone him, and they reply (verse 33) that it's for blasphemy — "because you, being a man, make yourself God."

Finally, I want to address one other point in what you said:

> Christianity, if you ask anyone besides a christian, is polytheistic.

It's true that if you ask most people who are not Christians, most (not all, but most) will tell you that Christians worship three gods. But consider this: if you want to find out about Buddhist teaching, who would be a better source for explaining it to you correctly, a Buddhist, or a non-Buddhist? If you want to find out about Jewish teaching, who would be more informed about it, a religious Jew, or a non-Jew? (The word "Jew" is ambiguous, referring to both a religion and an ethnicity — so I use the term "religious Jew" to distinguish people who follow the religion from people who are ethnically Jewish but don't follow the Jewish religion). If you want to be well-informed about Islam, who would explain it to you better, a Muslim, or a non-Muslim? And if you want to understand what Christianity actually teaches, who's more likely to be correct about it, a Christian or a non-Christian?

P.S. To explain just a little further, the teaching of the Trinity is indeed one of the most complex teachings of Christianity to fully grasp, and there have been countless arguments and debates about it over the centuries. The council at Nicaea in AD 325, which formalized the Nicene Creed, did not completely settle that — some people continued to argue over the doctrine later — but it pretty well cemented the official church position. That the Father, the Son, and the Holy Spirit ("Holy Ghost" in older English texts, but "Holy Spirit" in modern English) are both three and one. The modern English translation of the Nicene Creed is probably worth quoting here (at least the relevant bits) so people can see what the actual teaching is:

"I believe in one God, the Father almighty ... I believe in one Lord Jesus Christ, the Only Begotten Son of God, born of the Father before all ages. God from God, Light from Light, true God from true God, begotten, not made, consubstantial [which means "of one being, of one nature"] with the Father ... I believe in the Holy Spirit, the Lord, the giver of life, who proceeds from the Father and the Son, who with the Father and the Son is adored and glorified ..." (Source: https://www.usccb.org/prayers/nicene-creed, though there are multiple translations, e.g. the translation I'm most familiar with says "of one being with the Father" rather than "consubstantial with the Father").

And before I quit writing this P.S., I want to mention one kind of awesome story about the council of Nicaea. Which is the story about what St. Nicholas allegedly did there. (Yes, the St. Nicholas whose life inspired the story of Santa Claus). Sadly, the story is probably not true, since Nicholas's name does not appear in any of the lists of attendees that have survived... but it's an awesome story anyway. The story goes that Arius was standing in front of the council arguing his position, which was that Jesus had not existed eternally, but was created by God the Father at one point. (The famous phrase is "There was a time when he was not".) That part is certainly historically true. What is likely not historical is the rest of the story: that Nicholas got so mad at Arius's denial of the divinity of Jesus that he got up and slapped (some sources say "punched") Arius in the face.

Which leads to this historical-humor variation on a famous American Christmas carol:

    He knows when you are sleeping,
    He knows when you're awake,
    He knows when you've denied the divinity of Christ,
    So if you're an Arian, DUCK!