I wrote: "There's another option: that everyone is right enough about the things the Holy Spirit cares about"
You replied: "So, no one disagrees on the Trinity? No one disagree on whether baptism is necessary? No one disagrees on whether faith alone is sufficient? No one disagrees on whether Jesus Christ was God? What, then, is necessary?"
It's not that people don't disagree about the Trinity, or whether baptism is necessary, or whether faith alone is sufficient, or whether Jesus Christ was God. They do. It may be that, although people care about these things, the Holy Spirit doesn't. Which may be why Jesus never spoke of the Trinity, why the unbaptized thief on the cross, and the unbaptized Enoch and Elijah all three went to heaven anyway.
What IS necessary?
Well, to know the full answer to that, we'd have to ask God, but I expect that we cannot go very far wrong when we listen to what Jesus himself actually had to say about the entirety of Scripture. Jesus synopsized it all and said what it meant. Maybe we should take our current Bible, pull the pages out - at least of the Old Testament anyway, since that's what Jesus was referring to - and just write the sentence that Jesus gave that synopsized what the whole thing meant, was intended to mean, was about, from the God's-eye view: "Love your neighbor as yourself, and love God above all - that is the entirety of the Law and the prophets." ("the Law and the prophets" being Jewish shorthand for the Torah and the rest of the Jewish scriptures).
Since Jesus was God, and that's what HE said the point was, maybe we should really get to the fundamentals and decide that loving your neighbor as yourself and loving God above all is what's necessary. And the rest isn't.