8:18 So I have taken the Levites instead of all the firstborn sons among the Israelites. 8:19 I have given the Levites as a gift to Aaron and his sons from among the Israelites, to do the work for the Israelites in the tent of meeting, and to make atonement for the Israelites, so there will be no plague among the Israelites when the Israelites come near the sanctuary.” 1
8:20 So Moses and Aaron and the entire community of the Israelites did this with the Levites. According to all that the Lord commanded Moses concerning the Levites, this is what the Israelites did with them. 8:21 The Levites purified themselves 2 and washed their clothing; then Aaron presented them like a wave offering before the Lord, and Aaron made atonement for them to purify them. 8:22 After this, the Levites went in to do their work in the tent of meeting before Aaron and before his sons. As the Lord had commanded Moses concerning the Levites, so they did.
1 sn The firstborn were those that were essentially redeemed from death in Egypt when the blood was put on the doors. So in the very real sense they belonged to God (Exod 13:2,12). The firstborn was one who stood in special relationship to the father, being the successive offspring. Here, the Levites would stand in for the firstborn in that special role and special relationship. God also made it clear that the nation of Israel was his firstborn son (Exod 4:22-23), and so they stood in that relationship before all the nations. The tribe of Reuben was to have been the firstborn tribe, but in view of the presumptuous attempt to take over the leadership through pagan methods (Gen 35:22; 49:3-4), was passed over. The tribes of Levi and Simeon were also put down for their ancestors’ activities, but sanctuary service was still given to Levi.
2 tn The verb is the Hitpael of חָטָּא (khatta’). In this stem the meaning of the root “to sin” is likely to be connected to the noun “sin/purification” offering in a denominative sense, although some would take it as a privative usage, “to remove sin.” The idea is clear enough: They performed all the ritual in order to purify themselves ceremonially.