There are apparent differences between Paul’s Gospel and the Gospels of Matthew, Mark, Luke, and most of John. In this period, Paul was persecuting Christians.
After his conversion, he focused on the finished work of the cross and a gospel of grace. He never spoke of having to keep the law or any form of legalism, nor did he teach the gospel of the kingdom.
Jesus sent the 12 apostles to the Jews, and they spoke repeatedly of the kingdom of God and Christ, as did the Lord. Paul taught primarily to the Gentiles and, to a lesser extent, the Jews. He spoke of the resurrection of the saints and the rapture of the faithful.
Paul’s letters were progressive works of learning. His earlier letters were milk, being spoon-fed to baby Christians. But, as the years passed, he revealed mysteries to the Gentile church, secrets hidden in eternity past but now revealed by the Holy Spirit, and only now did the church begin to mature, growing in knowledge and understanding.
After Paul passed away, John received more secrets and mysteries that God revealed to him in the book of Revelation. The four gospels spoke repeatedly of the kingdom of God, that Jesus was the long-awaited Messiah the Jews had been waiting for, and that He, as their King, was ready to bring in the kingdom. But the Jews rejected him and then killed him. Not all Jews were set aside, but the Lord did commission Paul to bring the gospel of salvation to the Gentiles.
Romans 11:1-2, “I (Paul) say then, Hath God cast away his (the Jews) people? God forbid. --- God hath not cast away his people which He foreknew.”
There has always been a remnant of faithful New Testament Jews, beginning with the twelve. The Christian church, consisting of believing Jews and Gentiles, is built upon this foundation.
Paul writes, Ephesians 2:21-22, “Now, therefore, you (Gentiles) are no more strangers and foreigners, but fellow citizens with the saints (Jews,) --- And are built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief cornerstone. In whom all the building fitly framed together (being joined together) groweth unto a holy temple (one body) in the Lord.”
1 Corinthians 3:10, Paul was called a wise master builder, “I (Paul) have laid the foundation, and another (others that follow) builds thereon.”
Another issue never found in the four gospels is the mention of “The body of Christ.” But in Paul’s later letters, he often refers to the body of Christ.
1 Corinthians 12:12-13-27, “For as the body is one, and hath many members, and all the members of that one body, being many, are one body: so also is Christ. For by one Spirit are we all baptized into one body, whether we be Jews or Gentiles, whether we be bond or free; and have been all made to drink into one Spirit.”
Verse 27, “Now you are the body of Christ, and members in particular.”
Ephesians 1:20-23-24, Jesus, raised by the Father, seated at His right hand, above all principality, power, might, dominion, and above every name, in this world, and the world to come. All things are now under His feet, and head of the church. The church (Jew and Gentile) is his body, the fullness of Jesus that fills all in all.
When that last Christian is saved, Jesus Christ Himself will be complete, one head, one body.