God used the encyclopedia knowledge Saul had of scripture. Paul never once spoke ill of anything God had done, Paul loved the Lord. Paul told us that Christ gave us the law through our hearts, a change from how the law was formerly given without one word against the Lord Paul loved.
And as you know, Paul had the powerful mindset and presence to do all that he did. Paul and king David . . . nobody else like them in all of the Bible. Two very fascinating characters.