The Priesthood
The priesthood is the function of the priest. The priest stands between God and men: he carries to God, in the name of men, the offering and the prayer, and he passes on to men what God gives, his pardon and his blessing. The word comes from the Latin sacerdos, bound to the sacred: the one who performs holy things. Greek distinguishes two words: hiereus (ἱερεύς), the one who offers the sacrifice, which the New Testament reserves for Christ and the baptised people, and presbyteros (πρεσβύτερος), “the elder,” from which the word “priest” comes and which names the ministers established by the apostles.
The priest, a mediator
Scripture defines the priest in a single sentence: “Every high priest is taken from among men and appointed to act on their behalf in the service of God, to offer gifts and sacrifices for sins.” Hebrews 5:1 The priest is taken from among men: he is one of them. He is appointed on their behalf: his office is a service. His domain is their relations with God: prayer, worship, all that binds the people to their Lord. His proper task is to offer sacrifices: to present to God a gift in the name of all, to adore him and obtain his pardon. This is the mediator: the one who stands between the two shores, God and his people, and joins them.
From the temple to the Cross
In the Old Covenant, God appointed Aaron and his sons, in the tribe of Levi, to offer in the temple, in the name of all, animal sacrifices endlessly repeated. To grasp what these sacrifices accomplished, one must know what impurity was under the Law. Contact with death or corruption (touching a corpse, certain diseases, the flow of blood) made the faithful unclean, and this uncleanness was not first of all a sin: it was a state that barred one from approaching the sanctuary, on pain of profaning it: “In this way you shall keep the sons of Israel apart from their uncleannesses, lest they die by defiling my Dwelling, which is in their midst.” Leviticus 15:31 The blood of animals and the ashes of the red heifer washed away precisely this state: they restored to the faithful ritual purity, sanctifying them “so that their flesh is clean,” Hebrews 9:13 that outward purity which reopened access to worship and allowed one to appear again before God. Sin itself remained, for it engages the free will: to turn away from God is an act of the heart, and only a reparation freely offered can answer for it. A slaughtered beast does not offer itself, it submits; its blood bears no obedience and no love, nothing that could redeem a guilty will: “for it is impossible for the blood of bulls and goats to take away sins.” Hebrews 10:4 Yet God commanded these offerings, and for a good: returning every year for the same sins, they kept the conscience awake and deepened the longing for a pardon still to come: “these sacrifices are a yearly reminder of sins.” Hebrews 10:3 Each slain victim thus foretold the true victim. Christ came to fulfil the priesthood. He made himself at once priest and victim: on the Cross, he offers to his Father, once for all, the one sacrifice that saves, the gift of his own life: “we have been sanctified, through the offering of the body of Jesus Christ, once for all.” Hebrews 10:10
According to the order of Melchizedek
This priesthood of Christ endures forever, foretold from afar by a figure of Genesis, Melchizedek: “Then Melchizedek, king of Salem, brought bread and wine. He was a priest of God Most High, and he blessed Abram.” Genesis 14:18-19 Genesis presents him without genealogy, without birth or death recorded: he appears without origin and vanishes without end, and the Epistle to the Hebrews reads in him the image of the eternal Priest. “Without father, without mother, without genealogy, without beginning of days or end of life, made like the Son of God, he remains a priest forever.” Hebrews 7:3 This very absence makes him the image of the eternal Priest, whose priesthood has neither beginning nor term; and the bread and wine he presents foretell the offering of the Eucharist. The oracle of the royal psalm had foretold it. “You are a priest forever, in the order of Melchizedek.” Psalm 110:4 The Epistle to the Hebrews draws from it Christ’s superiority over the ancient priesthood: Abraham, and in him the tribe of Levi, pays the tithe to Melchizedek and receives his blessing, for “it is the lesser who is blessed by the greater.” Hebrews 7:7; and this change of priesthood brings a change of the whole Law. “when the priesthood is changed, a change of Law necessarily follows.” Hebrews 7:12
The priesthood shared
From this one priesthood of Christ flows all Christian priesthood. Through baptism, all the faithful receive a priesthood: they can offer to God their whole life, their work, their joys and their sorrows, as a spiritual offering. “like living stones, let yourselves be built into a spiritual house, for a holy priesthood, to offer spiritual sacrifices pleasing to God through Jesus Christ.” 1 Peter 2:5 This is the common priesthood of all the baptised: “you are a chosen race, a royal priesthood.” 1 Peter 2:9 Within this people, Christ calls some to a particular priesthood: through ordination, the priest receives the power to act in the very person of Christ the Head, in persona Christi, to make present, in the Eucharist, his one sacrifice. This is the ministerial priesthood, given to serve the common priesthood, and received in three degrees, the bishop, the priest, and the deacon, treated in the article on holy orders.
The same priest acts also in the other direction of mediation. Offering the Eucharist, he speaks in the name of the whole Church, in persona Ecclesiae: he presents to God the prayer, the thanksgiving and the offering of the assembled people. The two directions announced thus meet in him: he makes Christ present to his people, and he carries that people to God.
One single reality
The word “priesthood” thus goes back entirely to Christ, the one high priest who offered himself. “we have a great high priest who has passed through the heavens, Jesus the Son of God.” Hebrews 4:14 The baptised share in his priesthood by offering their lives; the ordained share in it otherwise, by making present his sacrifice. These two participations do not differ as more and less of one same thing: they differ in nature. The Second Vatican Council teaches that the common priesthood of the faithful and the ministerial priesthood “differ in essence and not only in degree,” while being ordered to one another. All goes back to Christ, the one mediator. “there is one God, and one mediator between God and mankind: a man, Christ Jesus.” 1 Timothy 2:5