The new Catholic Catechism contains not only what we believe in doctrine but also the program of how these are to implemented and embodied in the lives of successive generations of Christians. Jesus set this program up before He ascended into Heaven. We see the first part of the program in His final words directing them to baptize all nations (Matthew 28:19).
The Apostles understood more about all of this when each one received the Holy Spirit at Pentecost. Strengthened by this mission, the apostles “went forth and preached everywhere, while the Lord worked with them and confirmed the message by the signs that attended it.” (Mk. 16:20) This missionary effort has been persist in the successors of the Apostles in successive generations. And it will continue to the end of time as Jesus works to implement the fruits of His redemption.
In this new age of the Church after Christ ascended into Heaven, He now lives and acts in His Church through the sacraments. It is described by the Church as acting through the “sacramental economy” or “sacramental dispensation.” That is why the Church explains that Christ is really the one who acts through the sacraments, In Baptism, it is Christ who does the baptising; in Reconciliation, it is Christ who forgives sin and so in each sacrament. The role of the minister is necessary but he acts “in the person of Christ.” This is possible because Christ is living only in the present as God. There is no past or future with God, only the present. That is why the Mass is not a representation of the offering of Christ on the cross but the actual offering. This concept and actuality are beyond our human ability to understand it completely.