Commentary for Numbers 1:4

ואתכם יהיו AND WITH YOU THERE SHALL BE [A MAN OF EVERY TRIBE] — when you number them there shall be with you the princes of each tribe.

איש ראש לבית אבותיו, this is emphasised to show that no one challenged the authority and authenticity of the people representing themselves as the “heads of his family.” When the count occurred, אתכם in the presence of the family heads each one testifying to the age of the individuals concerned, no one would dare to challenge the accuracy of the data provided by the family head.

When you count them, there shall be with you. One might ask: From where does Rashi know this? Perhaps they should be with you for other matters, but not when you count them. Furthermore, from where does he know that the Torah refers to the leaders of the tribes, perhaps it refers to other people? The answer is: Since it is later written “these are the ones called from the congregation, the leaders of their fathers’ tribes” (v. 16), one can infer that they were the leaders of the tribes. Furthermore, it is written “Moshe and Aharon took these men … and they gathered together the entire congregation” (vs. 17-18) from there one may infer that they did the counting along with Moshe.