Bible Notes Online - Numbers 3 - ESV
Commentary

v1: This period, between the arrival at Sinai, and moving on, was important, as God laid down many instructions for their daily living.

v2-4: Eleazar and Ithamar, being the two surviving sons, served under Aaron, just as Joshua served under Moses.

v5-13: Special role and responsibilities for the Levites.

v6: The first role of the Levites was to assist Aaron, as High Priest.

v7: They also had to attend to the needs of the whole nation.

v8: They also had to look after the fabric of the Tabernacle.

v9-10: The Levites were appointed by God to serve with Aaron. This was an exclusive role, as others were not allowed to approach the Tabernacle in the same way.

v11-13: The Levites were to be the Lord's. This may follow from their support of Moses in Ex 32.26,28, when they rallied to Moses at the golden calf incident. Here they are to be joined to God in a special way, even as the first born had been redeemed in Egypt.

v14-20: The Levites were therefore to be numbered, not for war, but for service. We note that there were much fewer of them than of the other tribes, see v39. They were numbered from one month old; for all belonged to Levi, meaning ‘joined.’

v21-26: The family of Gershon, totalling 7,500. They camped behind the Tabernacle, out of sight of all who came to worship, yet their work was important; compare 1 Cor 12.22-24. We must be faithful in our service even when we are not seen by men.

v27-32: The Kohathites looked after the precious things of the tabernacle. This was more 'glamorous', yet also more dangerous, as some errors could be fatal, as Nadab and Abihu found (Lev 10).

v33-37: The family of Merari, totalling 6,200. Their responsibility was the fabric of the tent itself, which was heavy work. This was to do with foundations, which are essential.

The different numbers here are genuine not rigged. We would not expect this if the figures were invented.

These verses highlight the importance of 'practical' work. Without the Merarites faithfully carrying the fabric of the tabernacle, the whole pattern of worship would have stalled. Thus, God gives 'practical' tasks for His people to fulfil. It is not demeaning to think in these terms.

v38: Aaron and his sons, with Moses, had to be responsible for the care of the sanctuary.

v39: The Levites numbered 22,000, including those from one month old; far fewer than the other tribes.

v40-43: The number of first born males was counted, from a month old, so comparing like with like. They were to be 'swapped' with the Levites (v12-13).

v44-48: The excess of 273 had to be redeemed, for the Lord does 'obey His own rules'. This teaches the people that there is a correct way to do things.

See also my blog on the division of labour amongst the three Levite tribes: Service & Organisation (biblenotes.org.uk)