26 A bishop marked with the fullness of the sacrament of Orders, is "the steward of the grace of the supreme priesthood," especially in the Eucharist, which he offers or causes to be offered, and by which the Church continually lives and grows. This Church of Christ is truly present in all legitimate local congregations of the faithful which, united with their pastors, are themselves called churches in the New Testament. For in their locality these are the new People called by God, in the Holy Spirit and in much fullness. In them the faithful are gathered together by the preaching of the Gospel of Christ, and the mystery of the Lord's Supper is celebrated, that by the food and blood of the Lord's body the whole brotherhood may be joined together. In any community of the altar, under the sacred ministry of the bishop, there is exhibited a symbol of that charity and "unity of the mystical Body, without which there can be no salvation." In these communities, though frequently small and poor, or living in the Diaspora, Christ is present, and in virtue of His presence there is brought together one, holy, catholic and apostolic Church. For "the partaking of the body and blood of Christ does nothing other than make us be transformed into that which we consume". Every legitimate celebration of the Eucharist is regulated by the bishop, to whom is committed the office of offering the worship of Christian religion to the Divine Majesty and of administering it in accordance with the Lord's commandments and the Church's laws, as further defined by his particular judgment for his diocese. Bishops thus, by praying and laboring for the people, make outpourings in many ways and in great abundance from the fullness of Christ's holiness. By the ministry of the word they communicate God's power to those who believe unto salvation and through the sacraments, the regular and fruitful distribution of which they regulate by their authority, they sanctify the faithful. They direct the conferring of baptism, by which a sharing in the kingly priesthood of Christ is granted. They are the original ministers of confirmation, dispensers of sacred Orders and the moderators of penitential discipline, and they earnestly exhort and instruct their people to carry out with faith and reverence their part in the liturgy and especially in the holy sacrifice of the Mass. And lastly, by the example of their way of life they must be an influence for good to those over whom they preside, refraining from all evil and, as far as they are able with God's help, exchanging evil for good, so that together with the flock committed to their care they may arrive at eternal life.
Source: Lumen Gentium (Vatican.va)