Paul labours according to the ministry the Lord Jesus Christ gave him. He describes himself as being a minister of the dispensation of God, the mystery. In this passage he teaches the Colossians that he would have all of his audience be fully persuaded of and in acknowledgement of the mystery of God, and of the Father, and of Christ.
It is because of this mystery, that Gentiles who once had no hope can be saved without Israel, without Israel's law, and without Israel's covenants, by trusting in the finished work of Christ. Just as we've received Christ Jesus the Lord by faith, so also ought we to walk in Him (by faith).