The Sacrament of Holy Orders

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

(Catechism of the Catholic Church 1536).

The character of Jesus is given in a special way to those called by God to be Bishops, Priests, Deacons.
The Priest acts in the person of Jesus by teaching and explaining, by blessing and consecrating and by leading the communities of Faith, like Jesus the Good Shepherd.

Today the word "ordination" is reserved for the sacramental act which integrates a man into the order of bishops, presbyters, or deacons, and goes beyond a simple election, designation, delegation, or institution by the community, for it confers a gift of the Holy Spirit that permits the exercise of a "sacred power" (sacra potestas ) which can come only from Christ himself through his Church

(Catechism of the Catholic Church  1538).