179. Why did Christ institute an ecclesiastical hierarchy?
(Comp 179) Christ instituted an ecclesiastical hierarchy with the mission of feeding the people of God in his name and for this purpose gave it authority. The hierarchy is formed of sacred ministers; bishops, priests, and deacons. Thanks to the sacrament of Orders, bishops and priests act in the exercise of their ministry in the name and person of Christ the Head. Deacons minister to the people of God in the diakonia (service) of word, liturgy, and charity.
(CCC 935) To proclaim the faith and to plant his reign, Christ sends his apostles and their successors. He gives them a share in his own mission. From him they receive the power to act in his person.
To deepen and explain
(CCC 874) Christ is himself the source of ministry in the Church. He instituted the Church. He gave her authority and mission, orientation and goal: In order to shepherd the People of God and to increase its numbers without cease, Christ the Lord set up in his Church a variety of offices which aim at the good of the whole body. The holders of office, who are invested with a sacred power, are, in fact, dedicated to promoting the interests of their brethren, so that all who belong to the People of God… may attain to salvation (LG 18). (CCC 876) Intrinsically linked to the sacramental nature of ecclesial ministry is its character as service. Entirely dependent on Christ who gives mission and authority, ministers are truly "slaves of Christ" (Cf. Rom 1:1) in the image of him who freely took "the form of a slave" for us (Phil 2:7). Because the word and grace of which they are ministers are not their own, but are given to them by Christ for the sake of others, they must freely become the slaves of all (Cf. 1 Cor 9:19).
(CCC 875) "How are they to believe in him of whom they have never heard? and how are they to hear without a preacher? and how can men preach unless they are sent?" (Rom 10:14:15). No one - no individual and no community - can proclaim the Gospel to himself: "Faith comes from what is heard" (Rom 10:17). No one can give himself the mandate and the mission to proclaim the Gospel. The one sent by the Lord does not speak and act on his own authority, but by virtue of Christ's authority; not as a member of the community, but speaking to it in the name of Christ. No one can bestow grace on himself; it must be given and offered. This fact presupposes ministers of grace, authorized and empowered by Christ. From him, they receive the mission and faculty ("the sacred power") to act in persona Christi Capitis; deacons receive the strength to serve the people of God on the diaconia of liturgy, and charity, in communion with the bishops and his presbyterate. The ministry in which Christ's emissaries do and give by God's grace what they cannot do and give by their own powers, is called a "sacrament" by the Church's tradition. Indeed, the ministry of the Church is conferred by a special sacrament.