Adam Clarke on Numbers 26:2

Take the sum of all the congregation - After thirty-eight years God commands a second census of the Israelites to be made, to preserve the distinction in families, and to regulate the tribes previously to their entry into the promised land, and to ascertain the proportion of land which should be allowed to each tribe. For though the whole was divided by lot, yet the portions were so disposed that a numerous tribe did not draw where the lots assigned small inheritances. See Num 26:53-56, and also see the note on Num 1:1.