53 For, if you give careful consideration to all of the activity of a priest, what is the main point of his apostolate if not seeing to it that wherever the Church lives, a people who are joined by the bonds of faith, regenerated by holy Baptism and cleansed of their faults will be gathered together around the sacred altar? It is then that the priest, using the sacred power he has received, offers the divine Sacrifice in which Jesus Christ renews the unique immolation which He completed on Calvary for the redemption of mankind and for the glory of His heavenly Father. It is then that the Christians who have gathered together, acting through the ministry of the priest, present the divine Victim and offer themselves to the supreme and eternal God as a "sacrifice, living, holy, pleasing to God." (64) There it is that the people of God are taught the doctrines and precepts of faith and are nourished with the Body of Christ, and there it is that they find a means to gain supernatural life, to grow in it, and if need be to regain unity. And there besides, the Mystical Body of Christ, which is the Church, grows with spiritual increase throughout the world down to the end of time.
Source: Sacerdotii Nostri Primordia (Vatican.va)