What is the sacrament of Holy Orders?

Catechism of the Catholic Church: 1536

It 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.

Why is this sacrament called Holy Orders?

Catechism of the Catholic Church: 1537-1538

Orders designates an ecclesial body into which one enters by means of a special consecration (ordination). Through a special gift of the Holy Spirit, this sacrament enables the ordained to exercise a sacred power in the name and with the authority of Christ for the service of the People of God.

What place does the sacrament of Holy Orders have in the divine plan of salvation?

Catechism of the Catholic Church: 1539-1546,1590-1591

This sacrament was prefigured in the Old Covenant in the service of the Levites, in the priesthood of Aaron, and in the institution of the seventy “Elders”. These prefigurations find their fulfillment in Christ Jesus who by the sacrifice of the cross is the “one mediator between God and man”, the “High Priest according to the order of Melchizedek”. The one priesthood of Christ is made present in the ministerial priesthood.

“Only Christ is the true priest, the others being only his ministers.”

(Saint Thomas Aquinas)

What are the degrees that make up the sacrament of Holy Orders?

Catechism of the Catholic Church: 1554,1593

The sacrament of Holy Orders is composed of three degrees which are irreplaceable for the organic structure of the Church: the episcopate, the presbyterate and the diaconate.