When God established the Israelite covenant in Ex 19-23, there was no formal priesthood. The priests where the firstborn of each family.
However, very soon after the Israelite covenant, God then established the Levitical Covenant as defined and referenced in Lev 1-9, 16, 21-27 , Num 3, 4, 8, 18, 25:10-13, Deut 33:8-11, Neh 13:29, Mal 2:4-8.
The Levitical covenant is stated in Num 3:11-13, 25:12 where God takes the Levites (especially the line of Phineas as High Priest) instead of the all the firstborn of each family, thus changing the (informal) priesthood from the firstborn of each family to the (formal) priesthood of tribe of Levi. Several Bible writers refer to this Levitical Covenant including:
- Neh 13:29 – “the covenant of the priesthood and the Levites”
- Jer 33:18, 21 – “covenant with the Levitical priests.”
- Mal 2:4-8 – “the covenant with Levi”
- Num 25:10-13 – the eternal covenant of priesthood was also a covenant of peace and a covenant of “salt” (Num 18:19), ie, very solemn and eternal.
- Isa 54:10 & Eze 34:25 also describes the covenant of peace with the Levites
From other Bible passages we can see what the Levitical covenant was.
- The purpose of the Levitical covenant was to teach and inculcate the plan of salvation (Deut 33:9, 10, Heb 9:8, 9, 11-14, 10:1-3, Col 2:16, 17). That is, it symbolically taught about salvation by grace through the coming Messiah via His substitutionary death in the place of the sinner. Thus, the sacrifices, Levites, priests and High Priest became a type of Jesus in various ways.
- A promise by God to set them apart, ie, make them “holy” (Num 3:12, 13), to be a substitute for the first born in Israel, and to have the primary responsibility for caring for the sanctuary, its ritual services and sacrifices, maintaining and transporting its equipment. Ex 32:25-29. In this way, they became the priests of Israel. All these regulations were contained in Lev 1-9, 16, 21-27.
- Thus, the Levites enjoyed a “blessed” (and privileged) status. Ex 32:29, Mal 2:5.
- The book of Leviticus (and Num 1 & 18) sets out the responsibilities of the Levites in operating the ceremonial rites and sanctuary services and caring for the sanctuary equipment. See also Num 1:53, 18:2, Deut 10:8, 31:9, 25, Josh 3:3, 2 Sam 15:24, 1 Chron 15:26.
- The token/sign (Heb: “oth”) of the Levitical covenant appears to have been the unleavened bread at the annual festival (Ex 13:6, 9, 16, Lev 24:8).
The formal change from family-firstborn-priests to Levitical priesthood was done using the mechanism of the redemption money as described (in detail) in Num 3:40-51 and Num 18:14-16.