Why does the Torah insert the (otherwise superfluous) word "Roshei Beis Avosam"?
Sifri: To teach us that they were were already leaders before they were appointed as Nesi'im. 1
Why does the Torah emphasize "Heim Nesi'ei ha'Matos"?
Rashi: It is with reference to the slavery in Egypt, when these same princes, who were appointed policemen to force their Jewish brothers to fulfill their quota of bricks, declined to do so, for which they were mercilessly beaten by the task-masters. They were now compensated by being chosen as leaders of their respective tribes.
What is the Torah referring to when it writes "Heim ha'Omdim al ha'Pekudim"?
Rashi: It means that they stood together with Moshe and Aharon when they counted Yisrael. 1
Seforno: When they stood by their respective tribes as they were being counted, they felt that some of the members of their tribe were suspected of having sinned. 2
Rashbam: They are the ones who were mentioned by name in Bamidbar, 1:5-15.
Targum Yonasan: They are the ones who were appointed leaders in Egypt.
Rashi and Rashbam: As the Torah stated in Bamidbar, 1:5-15. Refer to 7:2:151:1. Perhaps they also stood with Moshe and Aharon when they counted Yisrael the first time - in Ki Sisa. See Oznayim la'Torah.
Seforno: And because they were the princes, they agreed to stand in the breach and bring Korbanos on their behalf to atone for them (See also Chizkuni).
Rashi explains 'they stood... when they counted Yisrael.' But that was a month later?
Riva (citing R. Tam of Orleans): When Moshe wrote the Torah, they had already stood when they counted. 1
This is like "Kidmas Ashur" in Bereishis 2:14 - where the Torah is discussing before Ashur was even born, and it is referring to what the place will later be called - Kesuvos 10b.)
