Jamieson, Fausset and Brown on Numbers 26:2

2. Take the sum of all the congregation--The design of this new census, after a lapse of thirty-eight years, was primarily to establish the vast multiplication of the posterity of Abraham in spite of the severe judgments inflicted upon them; secondarily, it was to preserve the distinction of families and to make arrangements, preparatory to an entrance into the promised land, for the distribution of the country according to the relative population of the tribes.