When was the mystery of Paul's gospel revealed, and to whom?
The mystery of Paul's gospel was kept secret since the world began and was revealed when God made it known to Paul. According to Romans 16:25, this secret, comprising the whole circle of Paul's doctrines, was revealed to him, with deeper revelations later given in Ephesians and his prison epistles.
Les explains that Romans 16:25 concerns the revelation of the mystery, or secret, that was kept in the mind of God and kept secret since the world began. This mystery is the whole circle of Paul's doctrines, which were kept secret until God revealed them to Paul. Les suggests most of these revelations came out during Paul's three years at Sinai, and the deeper revelations come out in Ephesians. He then takes the listener to Ephesians chapter 3, noting that Paul's prison epistles may contain these deeper doctrines, possibly poured out while Paul sat in prison in Caesarea waiting to go to Rome.
Now to him that is of power to stablish you according to my gospel, and the preaching of Jesus Christ, according to the revelation of the mystery, which was kept secret since the world began,