Paul was not a witness in Jesus' earthly ministry. He never heard the elaboration of the parables by Jesus. Therefore, all his epistles should be tested to determine whether they complement the preaching of Jesus or not. Furthermore, any important theological concept cannot be based on Paul's epistles alone. Gospel is the filter one has to apply to his letters.
Jesus only taught Jews. God sent Him to the "lost sheep of the house of Israel." When Jesus sent out His 12 Apostles, he instructed them to preach the gospel to Jews. They were not to preach to the Gentile nations.
Later Peter was chosen to take the gospel to the Gentile nations (in a vision). That is when Peter said "And Peter opened his mouth and said: "Truly I perceive that God shows no partiality, 35 but in every nation any one who fears him and does what is right is acceptable to him." Acts 10 Peter converted the Gentile house of Cornelius.
Peter was either slow, or had a problem taking the gospel of Christ to the Gentile nations, I don't know, but Paul was then chosen by the authority of heaven to take the gospel to the Gentiles.
Paul's message was to Gentiles. The Gentile nations had never been under the law of Moses. They had never been taught the "ten commandments," or any of the other 613 laws of the Law of Moses. They did not have the Old Covenant Scriptures.
The Jews had the Old Covenant Scriptures. The faithful Jews were looking for their Messiah. The Gentiles had to be taught everything about the Messiah, even about which tribe of the Jews from which He was born into the world.
Paul's preaching was to Gentiles who had worshipped idols, had temple prostitutes and God only know what else they practiced. The Jews already knew the one True God. Gentiles were in ignorance of the "God that they ignorantly worshipped." Paul preached the gospel to them . . . . "Christ, and Him crucified."
Of course the message was different.
You would do a real service to God if you studied Scripture to find out what was on the Apostle Paul's resume', instead of dismissing him as insignificant. He was the only man qualified, the only one that could possibly have accomplished the mission that he was chosen by heaven for, in my opinion.