Psalm 82 & Yoruba

Reading Psalm 82 once again a human is referred to as a god. Now, I realize that the lower-case "g" differentiates this from the upper-case "G" God. I am reading a book right now about Yoruba which explains that some of the Orisa (deities/gods) used to be human similarly the Kemetians held similar beliefs. What then, is the difference between the beliefs at points which concern gods, angels, Orisha, or Pharaohs? They all held to some deity outside of one central God. Okay, so I hear you. Christians don't worship humans in any form as God. Okay, but wouldn't Christianity still be technically polytheistic? How? The trinity (a word that appears nowhere in scripture). Yes, Christ said, "I and the father are one", but he said it while physically standing on earth and later implied that his followers were part of that oneness also. What the heck does that mean? I find it strange that all of this stuff makes sense to some weird degree surrounded by like thinking people, but when you are alone to question what went on, it suddenly becomes very nonsensical. I guess in my absence from church and being instructed what to think, I have begun to find that religions have more in common than they care to admit.