If by Baptism all the faithful share in the priesthood of Christ and if the universal call to holiness is truly for everyone, why does the Church have an ordained ministry for men? It is indeed the case that all baptized persons are called to exercise their priesthood through participation, each according to their vocation, in Christ’s mission. Catholics can fulfill this role in a variety of ways. It may be as a spouse and parent and as a witness to Christian values in secular society. In these ways the faithful experience the unfolding of baptismal grace in their lives. However, born of this common priesthood and dedicated to its service is the ministry conferred by Holy Orders. The ministerial priesthood is a means by which Christ builds up and leads his Church.

The whole Church is a priestly people. Through Baptism all the faithful share in the priesthood of Christ. This participation is called the "common priesthood of the faithful." Based on this common priesthood and ordered to its service, there exists another participation in the mission of Christ: the ministry conferred by the sacrament of Holy Orders, where the task is to serve in the name and in the person of Christ the Head in the midst of the community.
[Catechism of the Catholic Church, n. 1591]

Thus, the ministerial priesthood and the common priesthood of all the baptized are two forms of participation in the priesthood of Christ. There were forms of priesthood and special ministry in the Old Testament. All of this finds its fulfillment in Jesus Christ through the unique sacrifice of the cross. Our Lord is the ‘one mediator between God and men’ (1 Timothy 2:5). This is the priesthood of Christ to which we have referred. This one priesthood is made present through the ministerial priesthood without diminishing the uniqueness of Christ’s priesthood. The appropriate analogy is with the Eucharist. Christ’s redemptive sacrifice on the cross is unique and accomplished once for all. Yet we believe it is made present in the Eucharistic sacrifice of the Church. So the priest of the new law acts in the person of Christ, although it is Christ himself who is present to his Church.

The ministerial priesthood differs in essence from the common priesthood of the faithful because it confers a sacred power for the service of the faithful. The ordained ministers exercise their service for the People of God by teaching (munus docendi), divine worship (munus liturgicum) and pastoral governance (munus regendi).
[Catechism of the Catholic Church, n. 1592]

There are two degrees of ministerial participation in the priesthood of Christ: the episcopacy and the presbyterate. The diaconate is not part of the ministerial priesthood but it is intended to help and serve those who form part of it. Together, the forms of priestly participation (episcopate and presbyterate) and the degree of service (diaconate) all receive the sacramental act of ‘ordination’ in the sacrament of Holy Orders. These are the forms of apostolic ministry. Holy Orders is therefore the sacrament through which the mission entrusted by Christ to his apostles continues to be exercised in the Church until the end of time.

The three degrees of the Sacrament of Holy Orders:
•    Episcopacy (Bishops)
•    Presbyterate (Priests)
•    Diaconate (Deacons)

Ordination marks the entering of a man into one of these degrees. But it is not akin to an election. Ordination is a sacramental act. It is a special consecration through which, by a gift of the Holy Spirit, the exercise of a sacred power is permitted in the name and by the authority of Christ in the service of the People of God. It is an investiture by Christ himself and the laying on of hands by the bishop constitutes the visible sign of ordination.

The effects of ordination differ according to the degree of order:

• Bishops – they receive the fullness of the sacrament. As Christ’s vicar for a particular Church they are asked to teach, sanctify and govern.

• Priests – they become co-workers of the bishop in a diocese. They are charged with announcing the Good News; celebrating liturgy, especially the Eucharistic which gives them strength for their ministry; and to be a pastor to the faithful.

• Deacons – they are asked to serve. They assist priests and bishops in the celebration of the divine mysteries. They proclaim the Good News and preach and engage in various ministries of charity.

Common to all three degrees in the Sacrament of Holy Orders is the conferral of an indelible spiritual character upon the recipient. The man is configured to Christ by a special grace of the Holy Spirit to serve as Christ’s instrument for his Church. Hence, any one degree of the sacrament cannot be repeated or conferred temporarily.