"Now I want you to know, brothers, that the gospel preached by me is not based on a human point of view. For I did not receive it from a human source and I was not taught it, but it came by a revelation from Jesus Christ."Paul knew the scriptures backwards, forwards, and sideways, and he knew the message of Christ; he spent much time persecuting the Christians and in the process learned about the Christians and what they believed. But even with all that knowledge, he didn't believe that Jesus was the son of God. He didn't think those scriptures pointed to Jesus. It took Christ speaking to him straight out of heaven for Paul to finally trust in Christ. Most of us don't have such a dramatic conversion experience.
In thinking about this further, though, I realized that we sort of do all have a similar experience. No matter how many times we've heard the gospel, no matter how much head knowledge we may have about God or the Bible, we cannot truly trust in Christ until the Holy Spirit begins to work in us.