Why did Paul need three years in Arabia if God revealed truth to him directly?
The three years served as preparation. Paul was steeped in Judaism and, being human, needed time to cleanse his thinking and behavior. A clear-cut understanding of truths never revealed before naturally took time, and he had to become skilled in proclaiming them to the Gentile world.
Les explains that people have asked why it would take so long if Saul of Tarsus, after his conversion on the road to Damascus, was led down over the wall and then by God to Mount Sinai in Arabia for three years. He gives several reasons: Saul was steeped in Judaism and, being just as human as the rest of us, likely needed time to cleanse his thinking and behavior under Judaism. On the other hand, giving him such a clear-cut understanding of things that had never been revealed before would naturally take time. He also had to be so prepared that when he came back from that Arabian experience and was ready to go out among the Gentile world, even among idolaters, he was skilled in what he was proclaiming. Les sees that as part and parcel of the three-year training time down in Arabia. Yet Paul makes it plain that all of this was revealed to him, and he took the responsibility of passing it out to the whole world.