I'm sorry if I didn't make myself clear in the OP, but when I referred to Paul's preaching, I was referring to what Paul said that Jesus didn't say. Paul wasn't just another Christian preacher repeating what Jesus said but was apparently unique in that he came up with doctrines that not only differed from what Jesus preached but are arguably in conflict with what Jesus said. Also, Paul's writings are recorded in the canon of the New Testament, something that most other Christians including Jesus himself didn't achieve. So please explain this rather odd fact.
Well even Jesus told his disciples that he had many more things to say to them but they could not bear them now. (John 16:12) So we shouldn't think that Jesus ever intended to stop speaking to his followers. Just because he went to heaven doesn't mean he stops talking. He sends the holy Spirit and speaks to them that way. In fact he says the Spirit of truth will "lead and guide" them into all truth. That strongly suggests that they have more to learn. It suggests that they have not yet reached "all truth". So they need the Spirit of truth to guide them. (John 16:13)
So I reason that there is no doubt some of the things they couldn't bear then are the same things Paul talked about. Because they were so revolutionary. Because at the time Jesus said "you can't bear them now" For example; they all still believed they must keep the Law of Moses to be saved. So if Jesus had told them at that time all the revelations that they would later learn ... Then they would have freaked out and they would not have understood.
As for Jesus not having his own writings in the Bible. I think that he didn't want to be a writer. He came to preach and teach. He expected his followers to write and they did. I think it's a good thing. Because the gospel is more about his person. I think if he actually wrote a book then that would take preemenince for people. But since it was his followers who wrote about him ... that points everything to him as it should. It takes the emphasis off of the book and on to Jesus himself.
It's like you can't really praise yourself. You have to let other people praise you.
As for what is arguably in conflict with what Jesus said. There is a few things that should be understood about that. First of all some of these conflicts can be explained by the fact that while Jesus was alive (before the resurrection) they were still all in the old Testament. So they were still under the Law of Moses. Even Jesus was. That means that some things Jesus taught had to do with that time period. The new Testament comes through his blood. (Matthew 26:28) So, there was no new Testament until
after he died on the cross and rose from the dead. That's why some things that Paul teaches might seem to contradict because he was teaching in the new Testament and Jesus was teaching during the old Testament.
That doesn't mean we throw everything Jesus taught away. It just means we understand what he means. So everthing he says is useful and most of it is still applicable. But we do know (if we study enough that is) the difference between the old and new Testaments.
Finally other seeming contradictions might just need more examination to work out. Even Peter said that many people who read Paul's writings twist them to their own destruction. (2 Peter 3:16) So, the writings of the Bible (and particularly many of the writings of Paul) are not always easy to understand. They need the guidance of the holy Spirit (1 Corinthians 2:14) and experience also is useful. (Hebrews 5:14) Experience could require years of studying with the help of the holy Spirit.
