On account of the zeal that the Levites had demonstrated against the idolatry that had occurred with the golden calf, God was pleased to set them apart for himself (see Exodus 32:26–29). The fact that God now chooses them as a substitute for the firstborn in Israel is both humbling and liberating for the whole nation. It is humbling, because God’s choice of Levi stands as a reminder of the sin of idolatry that Israel had committed at Mount Sinai. It is liberating, because it will no longer be required of the Israelites to pay the redemption price for their firstborn sons and firstborn livestock.
12 Voici, j'ai pris les Lévites du milieu des enfants d'Israël, à la place de tous les premiers-nés, des premiers-nés des enfants d'Israël; et les Lévites m'appartiendront.