What is the specific mystery among the Gentiles in Colossians 1:27?

Les explains that Colossians 1:27 speaks of a mystery, or secret, among the Gentiles: Christ in you, the hope of glory. He points out that statements like this are not found in the four Gospels, the Old Testament, or the rest of the Bible except Paul's epistles. God had dealt with Israel for over 2,000 years before Christ came, but dealing with Gentiles in this way had never been heard of before. This particular secret is part of the overall body of truth called the mysteries. Les then connects it to Romans 8:10, where if Christ be in you, the body is dead because of sin, because Adam and the flesh were under the curse and death came through the fall of man.