Numbers 1:2

Take ye the sum. The enumeration and classification of males was a wise step to ensure orderly arrangements for the encampment and for marching. That this was its purpose is suggested by the fact that the numbering was evidently completed by the 20th of the same month, the very day on which Israel set forth from the Wilderness of Sinai to journey to the Wilderness of Paran (ch. 10:11). There had been a previous enumeration, for the purpose of levying the half-shekel tax needed for the erection of the tabernacle (see Ex. 30:12; 38:26). This second numbering was less a census than an organizational procedure — a mustering of men of military age by tribes and smaller units, with a leader (Num. 1:4, 5) appointed for each tribe.

House of their fathers. Here the group is the family. The term may, however, be used for an entire tribe descended from one ancestor (ch. 17:2), or again, a division of a tribe (Num. 3:24; Ex. 6:14).

Their polls. Literally, “their skulls.” This is a term used to designate individuals.