Concept

Melchizedekian Priesthood

Intro

In Genesis 14, Abraham meets a mysterious figure named Melchizedek, who is described as "king of Salem" and "priest of God Most High." Melchizedek blesses Abraham, and Abraham gives him a tenth of his spoils. Then Melchizedek vanishes from the narrative.

A thousand years later, the psalm-writer of Psalm 110 declares of the coming Messiah, "You are a priest forever according to the order of Melchizedek." Centuries after that, the New Testament book of Hebrews picks up the thread and works out what it means.

The Melchizedekian priesthood is a different category from the Aaronic or Levitical priesthood that Israel knew. Aaron's priesthood was inherited by genealogy through the tribe of Levi. Melchizedek's was not inherited at all; he simply appears. Aaron's was strictly separate from kingship (the priestly tribe could not also be the royal tribe). Melchizedek combined both offices in one person. Aaron's priesthood was passed down generation by generation as priests died and were replaced. Melchizedek's, on the Hebrews reading, is eternal.

The book of Hebrews makes the load-bearing apologetic move. Jesus, the writer says, comes from the tribe of Judah, not Levi. That looks like a problem if you expected the Messiah to be a Levitical priest. But the writer answers: Jesus is not a Levitical priest. He is a priest after the order of Melchizedek, an older, deeper, royal-priestly order. And because that order is eternal, His priesthood does not pass to a successor. The Old Covenant priesthood and the legal system bound up with it have been superseded (Heb 7:11-12).

This page lays out the defining marks of the Melchizedekian priesthood, the texts in Genesis, Psalms, and Hebrews that develop it, and how the doctrine shapes the Christian argument that believers today are not under the Mosaic Law.

In full

The priestly order to which the Messiah belongs, "a priest forever according to the order of Melchizedek" (Psalms 110.4). Distinguished from the Levitical / Aaronic priesthood by its independence from genealogical descent, its union of royal and priestly office, its precedence over Abraham (and so over Levi), and its eternal duration. In the argument of Hebrews (and centrally in Are Christians Still Under The Law (ris3n)), the inauguration of Christ's Melchizedekian priesthood entails the supersession of the Levitical priesthood and, with it, the Mosaic legal system bound to that priesthood (Heb 7:11-12).

Defining marks

Non-Levitical / non-genealogical. Not inherited through Aaron's line; not bound by tribal descent (Heb 7:13-14: Christ "was descended from Judah, a tribe with reference to which Moses spoke nothing concerning priests").
Royal-priestly. Combines kingship and priesthood in one office (Melchizedek is "king of Salem" and "priest of God Most High," Gen 14:18). The Levitical order strictly separated kingly (Davidic / Judah) from priestly (Aaronic / Levi) lines.
Eternal. "Made not on the basis of a law of physical requirement, but according to the power of an indestructible life... You are a priest forever" (Heb 7:16-17). Unlike the Levitical priesthood, succession is not required because the priest does not die.
Greater than Abraham (and so than Levi). Melchizedek blessed Abram and received Abram's tithe (Gen 14:18-20). Hebrews argues the lesser is blessed by the greater, and that Levi (still "in the loins" of Abraham) effectively tithed through Abraham, establishing Melchizedek's superiority (Heb 7:4-10).
Predates Sinai. Melchizedek's priestly office is in operation centuries before the Mosaic Law institutes the Aaronic order, indicating that priestly mediation between God and humanity is not rooted in or limited to the Sinai covenant.

Christological fulfillment

Royal-priestly Messiah. Christ as both King (Davidic, Judahite) and Priest (Melchizedekian, not Levitical), the union the Old Testament could not realize within the Mosaic order.
Eternal high-priesthood. "He, on the other hand, because He continues forever, holds His priesthood permanently. Therefore He is able also to save forever those who draw near to God through Him, since He always lives to make intercession for them" (Heb 7:24-25).
Mediator of a better covenant. "By so much also Jesus has become the guarantee of a better covenant" (Heb 7:22). The Melchizedekian priest brings with him the New Covenant.
Once-for-all sacrifice. Where the Levitical priest offered repeated sacrifice for sin, Christ offered Himself once (Heb 7:27; Heb 9:25-28; Heb 10:11-14).

The change-of-priesthood / change-of-law inference

Are Christians Still Under The Law (ris3n) makes this its load-bearing move:

Heb 7:11-12, "If perfection was through the Levitical priesthood... what further need was there for another priest to arise according to the order of Melchizedek...? For when the priesthood is changed, of necessity there takes place a change of law also."
The argument: the Levitical priesthood and the Mosaic legal system are inseparably bound; Scripture itself appoints a new priesthood (Melchizedekian, in Christ); therefore the Law-system bound to the older priesthood is changed.

This inference is contested in scope (does "change of law" mean total replacement, or change of the priestly / cultic law only?) but is broadly affirmed in form across Christian traditions.

Tensions

Scope of "change of law." Supersessionist readings (ris3n) take it to entail full replacement of the Mosaic Law; Reformed readings restrict it to the cultic / ceremonial law that was inseparably bound to the Levitical priesthood, leaving the moral law in force.
Ministerial priesthood today. Catholic and Orthodox traditions hold a ministerial / sacramental priesthood ordained by Christ, often understood as participating in His Melchizedekian priesthood. Protestant traditions generally locate Christ's Melchizedekian priesthood uniquely in Him, with the universal priesthood of believers (1 Pet 2:9; Rev 1:6) replacing the mediating priest-class. ris3n's framing fits the latter.
Identity of Melchizedek. Whether Melchizedek is a typological human figure, a christophany, or an angelic / heavenly figure (Qumran's 11Q13 reads him as a heavenly redeemer). Mainstream Christian reading: typological human; the article assumes this.