1)
What are the implications of the term "Sa Es Rosh"?
1.
Oznayim la'Torah: Based on the Midrash Rabah which explains in Bamidbar, 1:2 that it is a Lashon of elevation, because Yisrael were elevated on account of it: Here too, after the episode of Ba'al Pe'or, where Yisrael dropped to a lower level, the current census raised them to their previous level.
2)
Why does the Torah insert the words "le'Veis Avosam"?