Among his other contributions:
(1) Paul either is the direct author of, or the aegis for, most of the Scripture penned subsequent to the Incarnation.
(2) Paul reprimands Peter and other apostles for for allowing themselves to be intimidated by the treacherous false apostle, James of Jerusalem, the half-brother of Christ Jesus; Galatians 2:11-21.
Paul paid dearly for his opposition to the false teaching of James. The first plot of James against Paul recorded in the Scripture was the exhortation of James that Paul appease the zealot mob by sponsoring Jews taking a vow; the account begins in Acts 21:18 and continues into the next chapter.
It is obvious that James repeatedly dispatched zealot Talmudic thugs to murder Paul; consider the remark of James concerning "many thousands of Jews there are which believe; and they are all zealous of the law." James is the "thorn in the flesh" -- the agent of the Adversary who, through his pack of thugs, delivered beatings to Paul, II Corinthians 12:7.
On one occasion the beating administered to Paul appears to have been so severe as to dislodge the eyeballs of Paul from their sockets; thus, the remarks of Paul in Galatians 4:13-15. Ever after, the eyesight of Paul was severely impaired, thus, remarks such as Galatians 6:11, I Corinthians 16:21, II Thessalonians 3:17, Philemon 1:19.
(3) Paul exposes the greatest and most successful subversive plot of the Talmudic Jew against the Christian Faith, which is implementation of a hierarchical system, Papistry, as a counterfeit of the Church. In the true Church, which soon was driven underground, the Shepherd of the Assembly answers directly and solely to the Lord, Christ Jesus. Paul terms the Papal system the "Mystery of Iniquity." Paul alone withstood and restrained the system, II Thessalonians 2:6; Paul (and not the Spirit of God or the Church) is "he who letteth."
In exposing James of Jerusalem as a false apostle and in documenting and opposing the Papal system being implemented by James and colleagues, Paul was serving the purpose of the Lord, which is to provide in the Scripture a warning for future generations of Christians. But it is the will of the Lord that the Papal system continue until the Resurrection, for by it the Lord rewards those who do not gladly embrace truth.
P.S. It hardly needs to be pointed out that the Book of James, which virtually all attribute to James of Jerusalem, gainsays the teaching of both Paul and Moses concerning Justification. The Book of James amounts to a primer in Talmudic thinking.