11 And the Lord said to Moses in the waste land of Sinai, in the Tent of meeting, on the first day of the second month, in the second year after they came out of the land of Egypt, 2 Take the full number of the children of Israel, by their families, and by their fathers' houses, every male by name; 3 All those of twenty years old and over, who are able to go to war in Israel, are to be numbered by you and Aaron.
Matthew Henry's Commentary on Numbers 1:1-3
Commentary on Numbers 1:1-43
(Read Numbers 1:1-43)
The people were numbered to show God's faithfulness in thus increasing the seed of Jacob, that they might be the better trained for the wars and conquest of Canaan, and to ascertain their families in order to the division of the land. It is said of each tribe, that those were numbered who were able to go forth to war; they had wars before them, though now they met with no opposition. Let the believer be prepared to withstand the enemies of his soul, though all may appear to be peace.