When did Paul receive the deeper doctrines for his prison epistles?
Paul's deeper prison-epistle doctrines were poured out by the Lord while he was imprisoned in Caesarea awaiting transfer to Rome. Much of his mystery doctrine came during three years at Sinai, while the deeper revelations appear in Ephesians. This followed the mystery being kept secret since the world began, then revealed to him.
Les teaches from Romans 16:25 that the mystery, the whole circle of Paul's doctrines, was kept secret since the world began until God revealed it to Paul. He suggests most of it came out during the three years at Sinai, while the deeper revelations come out in Ephesians. He then proposes that in Paul's prison epistles the Lord may have poured out all these deeper doctrines while Paul sat in prison in Caesarea waiting to go to Rome, before turning to Ephesians chapter 3.