Like the Sacrament of Matrimony, Holy Orders (or “Ordination”) confers to the one receiving it a particular mission in the Church which helps to build up the People of God. Such persons are “set apart” and are marked in an indelible way by the Holy Spirit for their mission. In a special way, the Church, the ecclesial body of Christ, asks for God’s blessing on those who will be a special sign of Christ’s presence to all the people of God.

Holy Orders is the sacrament through which the mission entrusted by Christ to his apostles continues to be exercised in the Church until the end of time: thus it is the sacrament of apostolic ministry. It includes three degrees: episcopate, presbyterate, and diaconate…it confers a gift of the Holy Spirit that permits the exercise of a ‘sacred power’ which can come only from Christ himself through his Church.
CATECHISM, 1536 & 1538

Those ordained as bishops possess the fullness of the priesthood of Jesus Christ. Priests share in the priesthood of Christ and assist the bishops in their ministry. Deacons are configured in a particular way to Jesus Christ the servant.