It must have been a great joy to the heavenly host, even as contemplation of it was a great joy to Jesus himself.

"For the joy that was set before him [he] endured the cross, despising the shame, and is set down at the right hand of the throne of God." (Hebrews 12:2) What joy must have filled the hearts of his disciples when they began to understand the mystery of God and to see how wonderfully he had led them and their fathers before them, preparing them now for the revelation of this great truth! [312]In due time Saul of Tarsus, who afterward was named St.Paul, was illuminated and understood.

And then he wrote: "Who now rejoice in my sufferings for you, and fill up that which is behind of the afflictions of Christ in my flesh for his body's sake, which is the church: whereof I am made a minister, according to the dispensation of God which is given to me for you, to fulfill the word of God; even the mystery which hath been hid for ages and from generations, but now is made manifest to his saints: to whom God would make known what is the riches of the glory of this mystery among the gentiles; which [mystery] is Christ in you, the hope of glory." (Colossians 1:24-27) The Apostle here emphasizes the fact that this mystery of God is now made known only to the saints.
Saints means purified ones, which purification comes through receiving the merit of Christ's sacrifice.
[313]The word Christ signifies anointed.

Anointing means designation to official position in God's arrangement.

The Christ is the instrument or channel for the blessing of mankind.