John Calvin Commentary Numbers 3:1

"Now these are the generations of Aaron and Moses in the day that Jehovah spake with Moses in mount Sinai." — Numbers 3:1 (ASV)

These also are the generations of Aaron and Moses. He now separately enumerates the Levites; but, before stating their number, he first briefly refers to what he had previously narrated more fully: that of Aaron’s four sons, only two survived their father, since Nadab and Abihu had suffered the penalty for their negligence in defiling the sacrifice.

The six verses⁴²³ that Moses inserts regarding the office of the priests were explained in their proper place. The dignity of the tribe of Levi is exalted here, as God compares the Levites to the first-born; the distribution of their duties⁴²⁴ is also touched upon.

However, since these things are connected with the census of the people and the mode of pitching the camp, I have thought it best to connect them to what has just preceded, because otherwise the history would be interrupted. Indeed, in the order I have followed, the office of each family is only treated incidentally, so that all might know their proper station.

⁴²³ Viz., verses 5-10. See ante, vol. 2, p. 220..

⁴²⁴ “Quant a ce que Moyse touche ici des charges particulieres de chacune famille, combien que cela concerne le service duquel il a este traitte sur le Seconde Precepte, toutefois je n’ay peu aucunement faire, que de la mettre ici, afin que le fil de l’histoire ne fust point rompu;” with respect to the reference here made by Moses to the peculiar charge of each family, although it relates to the service which has been treated of under the Second Commandment, nevertheless I could not do otherwise than introduce it here, in order that the thread of the history might not be interrupted. — Fr..