We have here the speedy execution of the orders given for the numbering of the people. It was begun the same day that the orders were given, The first day of the second month; compare Num 1:18 with Num 1:1. Note, When any work is to be done for God it is good to set about it quickly, while the sense of duty is strong and pressing. And, for aught that appears, it was but one day's work, for many other things were done between this and the twentieth day of this month, when they removed their camp, Num 10:11. Joab was almost ten months numbering the people in David's time (Sa2 24:8); but then they were dispersed, now they lived closely together; then Satan proposed the doing of it, now God commanded it. It was the sooner and more easily done now because it had been done but a little while ago, and they needed but review the old books, with the alterations since made, which probably they had kept an account of as they occurred.
In the particulars here left upon record, we may observe, 1. That the numbers are registered in words at length (as I may say), and not in figures; to every one of the twelve tribes it is repeated, for the greater ceremony and solemnity of the account, that they were numbered by their generations, after their families, by the house of their fathers, according to the number of the names, to show that every tribe took and gave in the account by the same rule and in the same method, though so many hands were employed in it, setting down the genealogy first, to show that their family descended from Israel, then the families themselves in their order, then dividing each family into the houses, or subordinate families, that branched from it, and under these the names of the particular persons, according to the rules of heraldry. Thus every man might know who were his relations or next of kin, on which some laws we have already met with did depend: besides that the nearer any are to us in relation the more ready we should be to do them good. 2. That they all end with hundreds, only Gad with fifty (Num 1:25), but none of the numbers descend to units or tens. Some think it was a special providence that ordered all the tribes just at this time to be even numbers, and no odd or broken numbers among them, to show them that there was something more than ordinary designed in their increase, there being this uncommon in the circumstance of it. It is rather probable that Moses having some time before appointed rulers of hundreds, and rulers of fifties (Exo 18:25), they numbered the people by their respective rulers, which would bring the numbers to even hundreds or fifties. 3. That Judah is the must numerous of them all, more than double to Benjamin and Manasseh, and almost 12,000 more than any other tribe, v. 27. It was Judah whom his brethren must praise because from him Messiah the Prince was to descend; but, because that was a thing at a distance, God did in many ways honour that tribe in the mean time, particularly by the great increase of it, for his sake who was to spring out of Judah (Heb 7:14) in the fulness of time. Judah was to lead the van through the wilderness, and therefore was furnished accordingly with greater strength than any other tribe. 4. Ephraim and Manasseh, the sons of Joseph, are numbered as distinct tribes, and both together made up almost as many as Judah; this was in pursuance of Jacob's adoption of them, by which they were equalled with their uncles Reuben and Simeon, Gen 48:5. It was also the effect of the blessing of Joseph, who was to be a fruitful bough, Gen 49:22. And Ephraim the younger is put first, and is more numerous than Manasseh, for Jacob had crossed hands, and foreseen ten thousands of Ephraim and thousands of Manasseh. The fulfilling of this confirms our faith in the spirit of prophecy with which the patriarchs were endued. 5. When they came down into Egypt Dan had but one son (Gen 46:23), and so his tribe was but one family, Num 26:42. Benjamin had then ten sons (Gen 46:21), yet now the tribe of Dan is almost double in number to that of Benjamin. Note, The increasing and diminishing of families do not always go by probabilities. Some are multiplied greatly, and again are diminished, while others that were poor have families made them like a flock, Psa 107:38, Psa 107:39, Psa 107:41; and see Job 12:23. 6. It is said of each of the tribes that those were numbered who were able to go forth to war, to remind them that they had wars before them, though now they were in peace and met with no opposition. Let not him that girdeth on the harness boast as though he had put it off.

And they assembled all the congregation together on the first day of the second month,.... The month Ijar, as the Targum of Jonathan, answering to part of April and May: this was done on the selfsame day the Lord spake unto Moses about this affair, Num 1:1; so expeditious were he and Aaron in doing the will of God:

and they declared their pedigrees; either Moses and Aaron, according to Aben Ezra, who inquired when they were born, because of the computation of twenty years; and then their birth was wrote down, as he says; or rather the people declared their pedigrees, of what tribe, family, and house they were, who their parents, when born, and so, of course, how old they were; Jarchi interprets it, they brought the books of their genealogies, and witnesses to confirm the birth of everyone of them, to show their genealogy according to their tribe; nor is it at all unlikely that every family and house, or master thereof, kept a register of those born to him in it, whereby their age could be ascertained as well as pedigree:

after their famines, by the house of their fathers, according to the number of their names, from twenty years old and upwards, by their poll: that is, every tribe gave an account of the families in it, every family what houses were in it, and every house what number of males were in it, and of what age; and such were numbered who were twenty years old and upward.

by their polls--individually, one by one.