Where did Paul receive most of the doctrines of the mystery?
Paul received most of the doctrines of the mystery during the three years at Sinai. The deeper revelations came out later in Ephesians, and the Lord may have poured out these deeper doctrines while Paul sat in prison in Caesarea waiting to go to Rome.
Les teaches that the mystery, the whole circle of Paul's doctrines, was kept secret since the world began until God revealed it to Paul. He says most of it came out during those three years at Sinai, and then the deeper revelations came out in Ephesians. Les also suggests that the Lord may have poured out all these deeper doctrines while Paul was in prison in Caesarea waiting to go to Rome, and he then directs attention to Ephesians chapter 3.