The priesthood of Melchizedek is a role in Abrahamic religions, modelled on Melchizedek, combining the dual position of king and priest.
Melchizedek is a king and priest appearing in the Book of Genesis. The name means "King of Righteousness" - a name echoing kingly and priestly functions. He is the first individual to be given the title Kohen (priest) in the Hebrew Bible.
In the King James Version, the Book of Psalms names Melchizedek as representative of the priestly line through which a future king of Israel's Davidic line was ordained. Alternatively, it is suggested this term was here intended to be treated as an agglutinated improper noun, and thus translated as rightful king rather than left as Melchizedek; this interpretation is taken by some modern translations, such as the New JPS Tanakh.
The Law of Moses stipulates that only the male descendants of Aaron be commissioned to serve as Jewish priests before the God of Israel and the Jewish nation. This commission is believed in Judaism to be "a covenant of everlasting priesthood" ("Brith HaKehuna") and not eligible for replacement by other tribes of Israel.
Judaic midrash (exegesis) identifies Melchizedek with Shem the son of Noah. Although the Book of Genesis affirms that Melchizedek was "priest of God Most High". (Genesis 14:18), The Midrash and Babylonian Talmud maintain that the priesthood held by Melchizedek, who pre-dated the patriarch Levi by five generations (Melchizedek pre-dates Aaron by six generations; Abraham, Isaac, Jacob, Levi, Kehoth, Amram, Aaron) was given in his stead to Abraham who in turn passed it on to his patrilineal descendents, Isaac and then to Jacob. Midrashic literature attributes this transition as a consequence due to Melchizedek preceding the name of Abraham to that of God, such as in the Midrash Rabbah to Genesis. Tractate Nedarim. While some Jewish commentators, such as Chaim ibn Attar, write that Melchizedek gave the priesthood to Abraham willingly.