Peter Pett's Commentary on the Bible
Numbers 3:2-4
Chapter 3 The Priests and the Levites.
In this chapter more information is given about the priests and Levites, those set apart by Yahweh to watch over His Dwellingplace. Their task was to watch over the holiness of the Sanctuary.
The Consecration of the Priests to Yahweh (Numbers 3:2; Numbers 3:10).
We are first given a summary of the priesthood as it then was, and their consecration. At this stage it can be seen why they would need assistance from the tribe of Levi. Apart from these five, soon to become three, no one apart from Moses was allowed within the Sanctuary, although the sons of these priests were no doubt already growing up. Aaron was by this time ‘well matured' (Exodus 7:7) and Eleazar and Ithamar were no doubt married and would have developing sons of their own. The priests would soon multiply. But as yet they were still few.
‘And these are the names of the sons of Aaron, Nadab the first-born, and Abihu, Eleazar, and Ithamar. These are the names of the sons of Aaron, the priests that were anointed, whom he consecrated to minister in the priest's office.'
The names of the anointed priests apart from Aaron are given, Nadab, Abihu, Eleazar and Ithamar. These were his natural born sons whom, at Yahweh's command, he had consecrated to minister with him in the priest's office. (Or the ‘he' may be Yahweh).
‘And Nadab and Abihu died before Yahweh, when they offered strange fire before Yahweh, in the wilderness of Sinai, and they had no children; and Eleazar and Ithamar ministered in the priest's office in the presence of Aaron their father.
But two of these four were slain ‘before Yahweh', in the Sanctuary precincts, because they treated the things of God lightly, offering non-holy incense (‘strange fire', that is, not in accord with God's commandments) before Him. In view of the fact that everything in Numbers 4 is described as being under the control of Eleazar and Ithamar it is clear that that event had already happened by this stage.