Paul speaks of the value of this mystery about God as if it were a treasure of material wealth. Alternate translation: "the greatness of the glory of this mystery"
The mystery that God has made known is "Christ in you." Paul speaks of believers as if they were containers in which Christ is present. This is one of his ways of expressing the union of the believers with Christ. Alternate translation: "which is that Christ is in you" or "which is that Christ is united to you"
The fact that Christ is in believers gives believers hope that they will share in God's glory. Alternate translation: "so you can confidently expect to share in God's glory" or "so you can confidently wait for God's glory"