11 God spoke to Moses in the Wilderness of Sinai at the Tent of Meeting on the first day of the second month in the second year after they had left Egypt. He said, 2 "Number the congregation of the People of Israel by clans and families, writing down the names of every male. 3 You and Aaron are to register, company by company, every man who is twenty years and older who is able to fight in the army.
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.