3 and how the mystery was made known to me by revelation, as I wrote above in a few words, 4 a reading of which will enable you to perceive my understanding of the mystery of Christ. 5 In former generations this mystery was not made known to humankind, as it has now been revealed to his holy apostles and prophets by the Spirit: 6 that is, the Gentiles have become fellow heirs, members of the same body, and sharers in the promise in Christ Jesus through the gospel.
Matthew Henry's Commentary on Ephesians 3:3-6
Commentary on Ephesians 3:1-7
(Read Ephesians 3:1-7)
For having preached the doctrine of truth, the apostle was a prisoner, but a prisoner of Jesus Christ; the object of special protection and care, while thus suffering for him. All the gracious offers of the gospel, and the joyful tidings it contains, come from the rich grace of God; it is the great means by which the Spirit works grace in the souls of men. The mystery, is that secret, hidden purpose of salvation through Christ. This was not so fully and clearly shown in the ages before Christ, as unto the prophets of the New Testament. This was the great truth made known to the apostle, that God would call the Gentiles to salvation by faith in Christ. An effectual working of Divine power attends the gifts of Divine grace. As God appointed Paul to the office, so he qualified him for it.