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.

"The divinely instituted ecclesiastical ministry is exercised in different degrees by those who even from ancient times have been called bishops, priests, and deacons." 32 Catholic doctrine, expressed in the liturgy, the Magisterium, and the constant practice of the Church, recognizes that there are two degrees of ministerial participation in the priesthood of Christ: the episcopacy and the Presbyterate . the diaconate is intended to help and serve them. For this reason the term sacerdos in current usage denotes bishops and priests but not deacons. Yet Catholic doctrine teaches that the degrees of priestly participation (episcopate and presbyterate) and the degree of service (diaconate) are all three conferred by a sacramental act called "ordination," that is, by the sacrament of Holy Orders:

"Christ, whom the Father hallowed and sent into the world, has, through his apostles, made their successors, the bishops namely, sharers in his consecration and mission; and these, in their turn, duly entrusted in varying degrees various members of the Church with the office of their ministry." 43 "The function of the bishops' ministry was handed over in a subordinate degree to priests so that they might be appointed in the order of the priesthood and be co-workers of the episcapal order for the proper fulfillment of the apostolic mission that had been entrusted to it by Christ." 44

"The priests, prudent cooperators of the episcopal college and its support and instrument, called to the service of the People of God, constitute, together with their bishop, a unique sacerdotal college (Presbyterium) dedicated, it is, true to a variety of distinct duties. In each local assembly of the faithful they represent, in a certain sense, the bishop, with whom they are associated in all trust and generosity; in part they take upon themselves his duties and solicitude and in their daily toils discharge them." 51 priests can exercise their ministry only in dependence on the bishop and in communion with him. the promise of obedience they make to the bishop at the moment of ordination and the kiss of peace from him at the end of the ordination liturgy mean that the bishop considers them his co-workers, his sons, his brothers and his friends, and that they in return owe him love and obedience.