Even the mystery which hath been hid from ages and from generations, but now is made manifest to his saints: The mystery which hath been hid - The mystery is this: that God had designed to grant the Gentiles the same privileges with the Jews, and make them his people who were not his people. That this is what St. Paul means by the mystery, see Ephesians 3:3, etc.
Made manifest to his saints - It is fully known to all who have embraced the doctrine of Christ crucified; to all Christians.