I do see based only on scripture that Paul was an apostle and was converted, the problem I have is that Paul is indeed difficult to understand and easy to misinterpret. I see a huge difference in how the Message of Paul about his gospel to use his exact terms was compared to the Gospel as presented by Jesus. Because of this I tend to always go back to the words of Jesus or the other disciples/ apostles chosen by jesus and compare, I will give you an example how quickly things can go wrong
Justified by Faith
Gal 2:15 We
who are Jews by nature, and not sinners of the Gentiles,
Gal 2:16 Knowing that a man is not justified by the works of the law, but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified.
apparent contrast with James brother of Christ;
Faith Without Works Is Dead
Jas 2:14 What
doth it profit, my brethren, though a man say he hath faith, and have not works? can faith save him?
Jas 2:15 If a brother or sister be naked, and destitute of daily food,
Jas 2:16 And one of you say unto them, Depart in peace, be
ye warmed and filled; notwithstanding ye give them not those things which are needful to the body; what
doth it profit?
Jas 2:17 Even so faith, if it hath not works, is dead, being alone.
Jas 2:18 Yea, a man may say, Thou hast faith, and I have works: shew me thy faith without thy works, and I will shew thee my faith by my works.
Jas 2:19 Thou believest that there is one God; thou doest well: the devils also believe, and tremble.
Jas 2:20 But wilt thou know, O vain man, that faith without works is dead?
Jas 2:21 Was not Abraham our father justified by works, when he had offered Isaac his son upon the altar?
Jas 2:22 Seest thou how faith wrought with his works, and by works was faith made perfect?
Jas 2:23 And the scripture was fulfilled which saith, Abraham believed God, and it was imputed unto him for righteousness: and he was called the Friend of God.
Jas 2:24 Ye see then how that by works a man is justified, and not by faith only.
Jas 2:25 Likewise also was not Rahab the harlot justified by works, when she had received the messengers, and had sent
themout another way?
Jas 2:26 For as the body without the spirit is dead, so faith without works is dead also.
How do we reconcile this, see what I mean?