The priestly covenant (Hebrew: ברית הכהונה brith ha-kehuna) is the biblical covenant that God gave to Aaron and his descendants, the Aaronic priesthood, as found in the Hebrew Bible and Oral Torah.
The covenant is portrayed as everlasting and Halachically applicable notwithstanding the removal of the "five articles of honor" (see Jerusalem Talmud to Sotah 35b for the complete list) prior to the destruction of the First Temple, and most priestly duties, including Korban offerings- with the destruction of the Second Temple.
In the Torah, the covenant is cited as being compared to salt and is called "a covenant of salt forever" (Hebrew brith melach olam ברית מלח עולם), or "a statute forever" (Hebrew chukat olam"). In Midrashic sources the priestly covenant is one of five everlasting covenants.
The first person listed in the Hebrew Bible as a "priest" (Hebrew kohen) is Melchizedek. Midrashic literature details that due to Melchizedek preceding the name of Abraham to God, the priesthood was taken from him and given to Abraham who passed it on to his son Isaac who in turn passed it on to his son Jacob.
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 methods used by his forefather Abraham, to his brothers. He also instructed his sons to perpetuate this status of the tribe of Levi for eternity (Maimonides, On Idolatry 1:15). For the prelude of this choice see Targum Jonathan to Genesis 32:25, and 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 during their Egyptian Bonadage. Following his death, his post was assumed by his firstborn Aaron.