Catechism of the Catholic Church

1539 The chosen people was constituted by God as "a kingdom of priests and a holy nation." ⁶ But within the people of Israel, God chose one of the twelve tribes, that of Levi, and set it apart for liturgical service; God himself is its inheritance. ⁷ A special rite consecrated the beginnings of the priesthood of the Old Covenant. The priests are "appointed to act on behalf of men in relation to God, to offer gifts and sacrifices for sins." ⁸

1540 Instituted to proclaim the Word of God and to restore communion with God by sacrifices and prayer, ⁹ this priesthood nevertheless remains powerless to bring about salvation, needing to repeat its sacrifices ceaselessly and being unable to achieve a definitive sanctification, which only the sacrifice of Christ would accomplish. ¹⁰

1541 The liturgy of the Church, however, sees in the priesthood of Aaron and the service of the Levites, as in the institution of the seventy elders, ¹¹ a prefiguring of the ordained ministry of the New Covenant. Thus in the Latin Rite the Church prays in the consecratory preface of the ordination of bishops:

God the Father of our Lord Jesus Christ, . . .
by your gracious word
you have established the plan of your Church.

From the beginning,
you chose the descendants of Abraham to be your holy nation.
You established rulers and priests
and did not leave your sanctuary without ministers to serve you.... ¹²

1542 At the ordination of priests, the Church prays:

Lord, holy Father, . . .
when you had appointed high priests to rule your people,
you chose other men next to them in rank and dignity
to be with them and to help them in their task....

you extended the spirit of Moses to seventy wise men....
You shared among the sons of Aaron
the fullness of their father's power. ¹³

1543 In the consecratory prayer for ordination of deacons, the Church confesses:

Almighty God . . ..
You make the Church, Christ's body,
grow to its full stature as a new and greater temple.
You enrich it with every kind of grace
and perfect it with a diversity of members
to serve the whole body in a wonderful pattern of unity.

You established a threefold ministry of worship and service,
for the glory of your name.
As ministers of your tabernacle you chose the sons of Levi
and gave them your blessing as their everlasting inheritance. ¹⁴