Melchizedek Priesthood - in Judaism

In Judaism

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 "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, Issac, Jacob, Levi, Kehoth, Amram, Aaron) was given in his stead to Abraham who in turn passed it on to his patrilineal descendents, Issac and then to Jacob. Midrashic literature attributes this transition as a consequence due to Melchizedek preceding the name of Abraham to that of God, while some Jewish commentators, such as Chaim ibn Attar, write that Melchizedek gave the priesthood to Abraham willingly.

Maimonides, in his Mishna Torah compilation, explains that Jacob separated his son Levi from his other sons and appointed him to instruct and teach the ways of 'service to God', specifically the servicial methods used by his forefather Abraham, to his brothers. He also instructed his sons to perpetuate this status of Levi ("Shevet Levi") for eternity (Maimonides, Avodah Zorah 1:15). For the prelude of this choice see Targum Yonathan to Genesis 32:25, and/or Pirkei de-Rabbi Eliezer ch. 37. In midrash, it is written that Amram the son of Kohath the son of Levi was the spiritual leader of the sons of Jacob ("Israel") during their Egyptian Bondage. Following his passing, his post was assumed by his son Aaron.

At the time of the erection of the Tabernacle, God commanded Moses to appoint Aaron and his sons to the Jewish priestly service as a precondition to God revealing his Shechinah amongst the nation of Israel;

And Ahron and his sons I will sanctify to serve me and I will dwell amidst the sons of Israel and I will be to them a God, and they will know that I (am) God their Master that took them out from the land of Egypt (in order that) I (will) dwell in their midst —Exodus 29:44-46

King David in the Psalms refers to the future King of kings or Messiah as a "priest for ever after the order of Melchizedek." (Psalm 110:1-4.)