28 Christ, whom the Father has sanctified and sent into the world, has through His apostles, made their successors, the bishops, partakers of His consecration and His mission. They have legitimately handed on to different individuals in the Church various degrees of participation in this ministry. Thus the divinely established ecclesiastical ministry is exercised on different levels by those who from antiquity have been called bishops, priests and deacons. Priests, although they do not possess the highest degree of the priesthood, and although they are dependent on the bishops in the exercise of their power, nevertheless they are united with the bishops in sacerdotal dignity. By the power of the sacrament of Orders, in the image of Christ the eternal high Priest, they are consecrated to preach the Gospel and shepherd the faithful and to celebrate divine worship, so that they are true priests of the New Testament. Partakers of the function of Christ the sole Mediator, on their level of ministry, they announce the divine word to all. They exercise their sacred function especially in the Eucharistic worship or the celebration of the Mass by which acting in the person of Christ and proclaiming His Mystery they unite the prayers of the faithful with the sacrifice of their Head and renew and apply in the sacrifice of the Mass until the coming of the Lord the only sacrifice of the New Testament namely that of Christ offering Himself once for all a spotless Victim to the Father. For the sick and the sinners among the faithful, they exercise the ministry of alleviation and reconciliation and they present the needs and the prayers of the faithful to God the Father. Exercising within the limits of their authority the function of Christ as Shepherd and Head, they gather together God's family as a brotherhood all of one mind, and lead them in the Spirit, through Christ, to God the Father. In the midst of the flock they adore Him in spirit and in truth. Finally, they labor in word and doctrine, believing what they have read and meditated upon in the law of God, teaching what they have believed, and putting in practice in their own lives what they have taught. Priests, prudent cooperators with the Episcopal order, its aid and instrument, called to serve the people of God, constitute one priesthood with their bishop although bound by a diversity of duties. Associated with their bishop in a spirit of trust and generosity, they make him present in a certain sense in the individual local congregations, and take upon themselves, as far as they are able, his duties and the burden of his care, and discharge them with a daily interest. And as they sanctify and govern under the bishop's authority, that part of the Lord's flock entrusted to them they make the universal Church visible in their own locality and bring an efficacious assistance to the building up of the whole body of Christ. intent always upon the welfare of God's children, they must strive to lend their effort to the pastoral work of the whole diocese, and even of the entire Church. On account of this sharing in their priesthood and mission, let priests sincerely look upon the bishop as their father and reverently obey him. And let the bishop regard his priests as his co-workers and as sons and friends, just as Christ called His disciples now not servants but friends. All priests, both diocesan and religious, by reason of Orders and ministry, fit into this body of bishops and priests, and serve the good of the whole Church according to their vocation and the grace given to them. In virtue of their common sacred ordination and mission, all priests are bound together in intimate brotherhood, which naturally and freely manifests itself in mutual aid, spiritual as well as material, pastoral as well as personal, in their meetings and in communion of life, of labor and charity. Let them, as fathers in Christ, take care of the faithful whom they have begotten by baptism and their teaching. Becoming from the heart a pattern to the flock, let them so lead and serve their local community that it may worthily be called by that name, by which the one and entire people of God is signed, namely, the Church of God. Let them remember that by their daily life and interests they are showing the face of a truly sacerdotal and pastoral ministry to the faithful and the infidel, to Catholics and non-Catholics, and that to all they bear witness to the truth and life, and as good shepherds go after those also, who though baptized in the Catholic Church have fallen away from the use of the sacraments, or even from the faith. Because the human race today is joining more and more into a civic, economic and social unity, it is that much the more necessary that priests, by combined effort and aid, under the leadership of the bishops and the Supreme Pontiff, wipe out every kind of separateness, so that the whole human race may be brought into the unity of the family of God.
Source: Lumen Gentium (Vatican.va)