Why was God dealing with Gentiles such a new thing in the Bible?
God had been dealing with Israel for over 2,000 years before Christ came, so His direct dealings with Gentiles were previously unheard of. The mystery revealed in Paul's epistles—that Christ is in Gentiles, the hope of glory—was absent from the Gospels, the Old Testament, and the rest of Scripture.
Les teaches that this statement in Colossians 1:27 is unique. He says you will not find statements like this in the four Gospels—Matthew, Mark, Luke, and John—nor in the Old Testament, nor anywhere else in the Bible except Paul's epistles. God had dealt with Israel for over 2,000 years before Christ came, but now dealing with Gentiles had never been heard of before. This secret among the Gentiles belongs to the overall body of truth called the mysteries; this particular mystery is Christ in you, the hope of glory. Les then connects it to Romans 8:10: if Christ be in you, the body is dead because of sin, because the old Adam and the flesh are under the curse, and all men have to die unless the Lord comes to translate us.
To whom God would make known what is the riches of the glory of this mystery among the Gentiles; which is Christ in you, the hope of glory: