Why does the Torah insert the phrase "Vayikrav Aharon el ha'Mizbe'ach"?
Targum Yonasan: To teach us that, following Moshe's encouragement, Aharon overcame his fear and immediately approached the Mizbe'ach with Zerizus (alacrity).
Seeing as the people's Chatas did not comprise an Eigel, why did the Torah need to add the words "Asher Lo"?
Oznayim la'Torah #1: To teach us that, in spite of the fact that Yisrael partially shared in the Kaparah of his Chatas, 1 Aharon had to pay for it.
Oznayim la'Torah #2: To teach us that he only Shechted his own Chatas before his Olah, but not the Chatas of the people ? until afterwards, even though a Chatas generally precedes an Olah ? in order to first finish with his Kaparah before proceding with that of the people.
Oznayim la'Torah #3 (in Pasuk 12): Because he brought the Chatas specifically having in mind to atone for his sin ? which also explains why the Torah adds the word "Eigel ha'Chatas"
See Pasuk 2.
