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:
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:
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.