Read Colossians 1:27 Using Other Translations
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:
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.
For God wanted them to know that the riches and glory of Christ are for you Gentiles, too. And this is the secret: Christ lives in you. This gives you assurance of sharing his glory.