Which when the apostles, Barnabas and Paul, heard of, they rent their clothes, and ran in among the people Acts 14:14
I think the point of a discussion like this is the authority of God's Word. Paul wrote most of the books in the New Testament. The Holy Spirit witnesses that these words and revelations were given by God. God's Word doesn't lie no matter who the author is. Jesus said, I'm the Way the Truth and the Life. You don't discount Jesus' words because He testified about himself do you, the way the Pharisees did? Jesus said two witnesses were needed to verify the truth and said His Father and He were the two who witnesses who testified to the truth of what He was saying. So when Paul says in scripture which cannot lie, in Galatians 1:1, Paul, an apostle, (not of men, neither by man, but by Jesus Christ, and God the Father, who raised him from the dead;) , the Holy Spirit, the author of scripture, is the second witness (also the Father and the Body of Christ).
God called him (Paul) his instrument to take the gosple to gentiles etc, Acts 9 vs 15-16 does not say apostle...From Gods mouth to Ananias ear...He did not say he will be my apostle, tho he could have if he wanted to..God is not a man that he should lie.