What Luke wrote in his Gospel, he received from Paul; and what Paul received, he gained from the encounters he had with Jesus after His resurrection. Did Paul have more encounters than just on the road to Damascus?
Paul testifies that he was taught directly by Christ, and we see that in several places in Scripture. First, Paul says in 2 Corinthians that he had an audience with the Lord in the Heavenly throne room:
2Cor. 12:2 I know a man in Christ who fourteen years ago — whether in the body I do not know, or out of the body I do not know, God knows — such a man was caught up to the third heaven.
2Cor. 12:3 And I know how such a man — whether in the body or apart from the body I do not know, God knows —
2Cor. 12:4 was caught up into Paradise and heard inexpressible words, which a man is not permitted to speak.
2Cor. 12:5 On behalf of such a man I will boast; but on my own behalf I will not boast, except in regard to my weaknesses.
2Cor. 12:6 For if I do wish to boast I will not be foolish, for I will be speaking the truth; but I refrain from this, so that no one will credit me with more than he sees in me or hears from me.
2Cor. 12:7 Because of the surpassing greatness of the revelations, for this reason, to keep me from exalting myself, there was given me a thorn in the flesh, a messenger of Satan to torment me — to keep me from exalting myself!
Speaking in the third person (so as not to appear proud), Paul describes the moment he entered into Christ’s presence. Also, in Galatians 1 Paul testifies that he received the truth of the Gospel directly from Christ:
Gal. 1:10 For am I now seeking the favor of men, or of God? Or am I striving to please men? If I were still trying to please men, I would not be a bond-servant of Christ.
Gal. 1:11 For I would have you know, brethren, that the gospel which was preached by me is not according to man.
Gal. 1:12 For I neither received it from man, nor was I taught it, but I received it through a revelation of Jesus Christ.
We also have a record of Paul’s initial encounter with Jesus in Acts 9. Therefore, we know Paul’s knowledge was a result of Christ’s revelation to him directly.