Why should we believe anything Paul has to say? What kind’ve proof is his “vision” of Jesus? What true authority does Paul have? How do we know what he’s saying is true?
Clearly, his conversion convinced the Christians he was persecuting to the point that he was not only accepted among them, but became a leader himself.
Later on, his writings were deemed divinely inspired by the Church, and thus part of Holy Scripture - a decision that was made with the guidance of the Holy Spirit.
It is purely a matter of faith - there is no other reason to accept his writings.
His teaching was confirmed by the Apostles. His authority was given by God and confirmed by the Apostles.
See the book of Acts.
Anything in the Bible written by Paul was done so while the Apostles were still alive so it could be accepted into the New Testament Canon as long as the writings could be authenticated and did not contradict Sacred Tradition. Public revelation ended with the death of John the Apostle, so anything written after that point could not be considered Sacred Scripture.
Immediately after his conversion he followed the Lord’s command, went to the apostles, submitted to their authority and further teaching, and allowed himself to prepared and guided in his ministry by their authority. He repeatedly referred and deferred to that authority during his ministry, and did not hesitate to challenge them when he felt they disregarded their own teaching. However in those cases he submitted to the judgment of the whole Church in council. His writings were accepted as inspired into the canon of scripture by the Catholic Church, so they are inspired. period.
I’ll let Paul himself answer your concerns:Are we beginning to commend ourselves again? Or do we need, as some do, letters of recommendation to you, or from you? You yourselves are our letter of recommendation, written on our hearts, to be known and read by all. And you show that you are a letter from Christ delivered by us, written not with ink but with the Spirit of the living God, not on tablets of stone but on tablets of human hearts.
Such is the confidence that we have through Christ toward God. Not that we are sufficient in ourselves to claim anything as coming from us, but our sufficiency is from God, who has made us competent to be ministers of a new covenant, not of the letter but of the Spirit. For the letter kills, but the Spirit gives life.
2 Corinthians 3:1-6
God sent Ananias to Saul, and God confirmed his conversion to Ananias. Similarly, the Holy Spirit told the Apostles to commission Paul and Barnabas.