Where can you not find many of Paul's doctrines?
Many of Paul's doctrines are absent from the Old Testament, from Christ's earthly ministry, and from the early portions of Acts. They were revelations God had kept secret since the beginning of human history, or even before, and were not previously revealed in any of God's dealings with mankind.
Les explains that if you want a good Bible study, take a concordance and look up the word mystery wherever it appears in Paul's epistles, making a two or three hour study of the concepts Paul associates with this revelation of a mystery. He emphasizes that these things from Paul's epistles were never revealed previously in any of God's dealing with mankind. So many of Paul's doctrines cannot be found in the Old Testament, in Christ's earthly ministry, or in the early parts of Acts. They were revelations God had kept secret since the beginning of human history, or even before. Les also points to Deuteronomy 29:29, where the secret things belong unto the Lord our God, because He is sovereign and Creator of everything.