Holy Orders is the sacrament through which the mission entrusted by Christ to his apostles continues to be exercised in the Church until the end of time: thus it is the sacrament of apostolic ministry. It includes three degrees: episcopate, presbyterate, and diaconate.
As stated in the Catechism of the Catholic Church: The whole Church is a priestly people. Through Baptism all the faithful share in the priesthood of Christ. This participation is called the "common priesthood of the faithful." Based on this common priesthood and ordered to its service, there exists another participation in the mission of Christ: the ministry conferred by the sacrament of Holy Orders, where the task is to serve in the name and in the person of Christ the Head in the midst of the community. The ministerial priesthood differs in essence from the common priesthood of the faithful because it confers a sacred power for the service of the faithful. The ordained ministers exercise their service for the People of God by teaching (munus docendi), divine worship (munus liturgicum) and pastoral governance (munus regendi). Since the beginning, the ordained ministry has been conferred and exercised in three degrees: that of bishops, that of presbyters, and that of deacons. The ministries conferred by ordination are irreplaceable for the organic structure of the Church: without the bishop, presbyters, and deacons, one cannot speak of the Church (cf. St. Ignatius of Antioch, Ad Trall. 3,1).
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