and on the first day of the second month they assembled the whole congregation and recorded their ancestry by clans and families, counting one by one the names of those twenty years of age or older,
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.
Commenting on Numbers 1:17-43
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...
by their polls--individually, one by one.