CATECHISM OF THE CATHOLIC CHURCH
SECOND EDITION

Paragraphs 1546–1549

1546 Christ, high priest and unique mediator, has made of the Church "a kingdom, priests for his God and Father." The whole community of believers is, as such, priestly. The faithful exercise their baptismal priesthood through their participation, each according to his own vocation, in Christ's mission as priest, prophet, and king. Through the sacraments of Baptism and Confirmation the faithful are "consecrated to be . . . a holy priesthood."
1547 The ministerial or hierarchical priesthood of bishops and priests, and the common priesthood of all the faithful participate, "each in its own proper way, in the one priesthood of Christ." While being "ordered one to another," they differ essentially. In what sense? While the common priesthood of the faithful is exercised by the unfolding of baptismal grace --a life of faith, hope, and charity, a life according to the Spirit--, the ministerial priesthood is at the service of the common priesthood. It is directed at the unfolding of the baptismal grace of all Christians. The ministerial priesthood is a means by which Christ unceasingly builds up and leads his Church. For this reason it is transmitted by its own sacrament, the sacrament of Holy Orders.
1548 In the ecclesial service of the ordained minister, it is Christ himself who is present to his Church as Head of his Body, Shepherd of his flock, high priest of the redemptive sacrifice, Teacher of Truth. This is what the Church means by saying that the priest, by virtue of the sacrament of Holy Orders, acts in persona Christi Capitis:

It is the same priest, Christ Jesus, whose sacred person his minister truly represents. Now the minister, by reason of the sacerdotal consecration which he has received, is truly made like to the high priest and possesses the authority to act in the power and place of the person of Christ himself (virtute ac persona ipsius Christi).

Christ is the source of all priesthood: the priest of the old law was a figure of Christ, and the priest of the new law acts in the person of Christ.

1549 Through the ordained ministry, especially that of bishops and priests, the presence of Christ as head of the Church is made visible in the midst of the community of believers. In the beautiful expression of St. Ignatius of Antioch, the bishop is typos tou Patros: he is like the living image of God the Father.