Why did Hashem see fit to insert this Pasuk?
Rashi: Hashem repeated the instructions (briefly), to render every detail crucial to Aharon and his sons' inauguration. 1
The Gemara in Yoma, 5a, learns this from the word "Kachah", which always implies that the issue under discussion is crucial.
In what respect is the Torah comparing Aharon and his sons?
Yerushalmi, Yoma, 7:3: To teach us that the Begadim (the Avneit) of the Kohen Hedyot contained Sha'atnez just like those of the Kohen Gadol. 1
What is the significance of the 'Hey' in the word "Osachah"?
Rashi (in Tehilim, 10:8): We have a tradition that on twenty-five occasions in Tanach, the Pasuk writes 'Chaf-Hey' instead of 'Chaf''.
Ha'Kesav ve'ha'Kabalah: The 'Hey' indicates desire.
Daf Al ha'Daf (Zevachim 102a, citing l'Levi Amar): The feminine form hints that Moshe's strength became weak, like a female. The seven days of the Milu'im correspond to the seven days that Moshe delayed at the burning bush; due to this, the Kehunah did not come from him, rather, from Aharon. Even so, Moshe was happy that his brother received Kehunah.
Which seven days is the Torah referring to?
Why does it say "Tzivisi Osachah", and not 'Tzivisicha'?
Panim Yafos: The commands to build the Mishkan Moshe can fulfill through a Shali'ach. However, he himself must offer the Korbanos and dress Aharon and his sons.