CIC 784 On entering the People of God through faith and Baptism, one receives a share in this people’s unique, priestly vocation: “Christ the Lord, high priest taken from among men, has made this new people ‘a kingdom of priests to God, his Father.’ The baptized, by regeneration and the anointing of the Holy Spirit, are consecrated to be a spiritual house and a holy priesthood.”1

CIC 1537 The word order in Roman antiquity designated an established civil body, especially a governing body. Ordinatio means incorporation into an ordo. In the Church there are established bodies which Tradition, not without a basis in Sacred Scripture,2 has since ancient times called taxeis (Greek) or ordines. And so the liturgy speaks of the ordo episcoporum, the ordo presbyterorum, the ordo diaconorum. Other groups also receive this name of ordo: catechumens, virgins, spouses, widows,...

CIC 1539 The chosen people was constituted by God as “a kingdom of priests and a holy nation.”3 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.4 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.”5

CIC 1540 Instituted to proclaim the Word of God and to restore communion with God by sacrifices and prayer,6 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.7

CIC 1564 “Whilst not having the supreme degree of the pontifical office, and notwithstanding the fact that they depend on the bishops in the exercise of their own proper power, the priests are for all that associated with them by reason of their sacerdotal dignity; and in virtue of the sacrament of Holy Orders, after the image of Christ, the supreme and eternal priest, they are consecrated in order to preach the Gospel and shepherd the faithful as well as to celebrate divine worship as true priests of the New Testament.”8

CIC 1578 No one has a right to receive the sacrament of Holy Orders. Indeed no one claims this office for himself; he is called to it by God.9 Anyone who thinks he recognizes the signs of God’s call to the ordained ministry must humbly submit his desire to the authority of the Church, who has the responsibility and right to call someone to receive orders. Like every grace this sacrament can be received only as an unmerited gift.

1 LG 10; Cf. Heb 5:1-5; Rev 1:6.
2 Cf. Heb 5:6; 7:11; Ps 110:4.
3 Ex 19:6; cf. Isa 61:6.
4 Cf. Num 1:48-53; Josh 13:33.
5 Heb 5:1; cf. Ex 29:1-30; Lev 8.
6 Cf. Mal 2:7-9.
7 Cf. Heb 5:3; 7:27; 101-4.
8 LG 28 cf. Heb 5:1-10; 7:24; 9:11-28; Innocent I, Epist. ad Decentium:PL 20,554A; St. Gregory of Nazianzus, Oratio 2,22:PG 35,432B.
9 Cf. Heb 5:4.