Why did Paul spend three years in Arabia?
Paul spent three years in Arabia to receive private instruction from the Lord Jesus Christ, ensuring he was not behind the twelve apostles in time spent with the Lord. This period at Mount Sinai gave him full authority and prepared him for the preaching he would do.
Les explains that Paul's opponents argued Peter and the others had three years with Jesus walking the dusty roads of Palestine, but Paul also had three years. He likely spent that time at Mount Sinai in private tutorage from the Lord Jesus Himself. It was not merely to learn what he would preach, but to give him the full authority of time spent with the Lord, so he was not one whit behind the twelve. Paul later defends his credentials in 2 Corinthians 11:22-23, claiming to be a Hebrew, an Israelite, and a seed of Abraham just as they were, with more abundant labors, stripes, prisons, and deaths.