Jim Jordan likes to talk about the "Enoch Factor." The phrase refers to the historical phenomenon laid out in Genesis 4.
Cain fathers Enoch and builds a city by the same name. In the line of Enoch are Jabal, the first animal husbandman, and Jubal, father of music, as well as Tubal-cain, the Bible's "Vulcan," father of metallurgy (Genesis 4:16-22).
All these things are good, and Israel assumes these tasks. In Israel there are shepherds, musicians, craftsmen who work with metals. Israel eventually becomes an urban civilization. In each case, though, the children of Cain got there first.
Jordan draws a larger conclusion: Pagans often get there first. They're the first to make cultural and political and technological breakthroughs. That shouldn't be a source of anxiety, for, as Solomon says, the wealth of the sinner is stored up for the righteous (Proverbs 13:22). Jesus is heir of all things, and He shares His inheritance with His body. Whatever advances the ungodly make, they'll ultimately serve Jesus, and us.
It's surprising to realize that there's an Enoch factor at work in the biblical history of priesthood. It's surprising because priestly service is the defining vocation of Israel. It's what Israel is called from Egypt to become, a "kingdom of priests."
But like so many other institutions and advances, priesthood first arises among the Gentiles. Melchizedek is the first priest of Scripture (Genesis 14:18). Joseph marries the daughter of an Egyptian priest (Genesis 41:45; 46:20), and we hear of other Egyptians priests (Genesis 47:22, 26). In the first half of the book of Exodus, only Jethro, Moses' father-in-law is a priest (Exodus 2:16; 3:1; 18:1).
Melchizedek and Jethro are priests to the "Most High God," the Creator who is identical with Yahweh the God of Israel. Perhaps even Potipherah the Egyptian priest is a convert to Yahweh. But these aren't Hebrews, part of Abraham's household. They aren't pagans, but they're Gentiles.
As far back as Adam, the patriarchs do priestly things. Adam is servant and guardian of the Garden, a priestly role. Abel offers sacrifice, and Noah offers the first ascension offering. Abraham builds altars and worships, and takes Isaac to Moriah to offer him as an ascension. Isaac and Jacob sometimes act like priests. But they are never called priests (kohen) and their activities are never described with the verb kahan.
This has mainly to do with the specific force of kohen in Scripture. A priest is a servant in the house of a god. Since Israel's God had no permanent residence before the tabernacle (the Enoch factor strikes again), Israel had no priests. They are called priests, and are given a priestly class, only when they are given instructions about a sanctuary.
The first time Israelites are called priests is at Sinai, when Yahweh designates them as a "kingdom of priests" (Exodus 19:6). Israel is Yahweh's firstborn son (Exodus 4:22-23) among the nations. Firstborn sons appear to have a leading cultic role in the patriarchal period. By virtue of the Exodus, Yahweh claims the firstborn sons as His own (Exodus 13).
Calling Israel "firstborn" already hints at Israel's priestly vocation among the nations, and Exodus 19 confirms it. (For an extensive discussion of the firstborn/priest connection, see Scott Hahn's Kinship by Covenant, ch. 6.)
Israel isn't simply a nation with priests. Every nation had priests. They aren't even merely a nation with priests of the living God. Salem and Midian at least had priests of the Most High God. What distinguishes Israel is its calling as a priestly nation, maintaining Yahweh's house on behalf of the Gentiles.
Though Israel is a kingdom of priests, some within Israel are designated as priests (Exodus 19:24), even before Aaron and his sons are selected. Who are they? Hahn argues they are the "young men" who offer ascensions and sacrifices (Exodus 24:5), which might be the firstborn sons redeemed at Passover.
These do not remain the "priests" within the priestly people. When Aaron leads the people in idolatry, Moses summons "whoever is for Yahweh" to come to him (Exodus 32:26). The Levites answer the summons, and they slaughter three thousand idolaters (Exodus 32:27-28).
Because of this act of zeal, the Levites are rewarded by receiving a grant of priesthood. They took swords in their hands, and so Moses "fills the hand" with priestly privilege (Exodus 32:27, 29). A formal transfer of priestly privilege from the firstborn to the Levites takes place in Numbers (3:44-51; ch. 8).
The golden calf incident appears to end the covenant with the priestly nation. Never again in the Old Testament is Israel called a "kingdom of priests." Israel still has a priestly role among the Gentiles, but it's now carried out by designated priests within Israel, by Aaron and his sons, along with the Levites.
Priestly privilege is narrowed further during Israel's wilderness sojourn. When Phinehas stops a plague by impaling a fornicating couple (Numbers 25), Yahweh grants Him a "covenant of perpetual priesthood" (v. 13). Even among the zealous tribe of Levi, Phinehas's zeal stands out.
It takes some time, but priestly status is eventually narrowed to the descendants of Phinehas. After Eli and Abiathar, the priesthood is transferred from the descendants of Aaron's son Ithamar to the descendants of Eleazar, Phinehas's father (Numbers 25:7, 11; 1 Chronicles 6:4). Solomon appoints Zadok to priest (1 Kings 2:35), from the line of Phinehas (1 Chronicles 6:4-8). (See the interesting, though sometimes speculative, discussion in Douglas van Dorn, Waters of Creation, Part III.)
In a sense, this priestly covenant persists beyond the Davidic. After there are no more descendants of David bearing the title "king," there are still Zadokite priests, who assume quasi-royal and quasi-prophetic responsibilities. Jesus comes to raise up David, but when He comes, the priests are still there. Over many centuries, the priestly covenant provides the main institutional continuity for Israel's worship and social life.
All this, and much more, is in the air when Yahweh commands Moses, "bring near to yourself Aaron your brother, and his sons with him . . . to priest to me" (Exodus 28:1).