Colossians 1:27-29 – To them God chose to make known how great among the Gentiles are the riches of the glory of this mystery, which is Christ in you, the hope of glory. 28 Him we proclaim, warning everyone and teaching everyone with all wisdom, that we may present everyone mature in Christ. 29 For this I toil, struggling with all his energy that he powerfully works within me.
“The OT predicted the coming of the Messiah and that the Gentiles would partake of salvation (cf. Is. 42:6; 45:21, 22; 49:6; 52:10; 60:1–3; Pss. 22:27; 65:5; 98:2, 3), but it did not reveal that the Messiah would actually live in each member of His redeemed church, made up mostly of Gentiles. That believers, both Jew and Gentile, now possess the surpassing riches of the indwelling Christ is the glorious revealed mystery (John 14:23; Rom. 8:9, 10; Gal. 2:20; Eph. 1:7, 17, 18; 3:8–10, 16–19). the hope of glory. The indwelling Spirit of Christ is the guarantee to each believer of future glory (Rom. 8:11; Eph. 1:13, 14; 1 Pet. 1:3, 4).” – Dr. John MacArthur