What is the significance of the term "Avodas Matanah"?
Rashi: Hashem gave the Avodah to the Kohanim as a gift.
Ramban: The Torah is teaching us here that the Avodas ha'Kehunah is not an onus, like the service of human kings, but a (precious) gift, which Hashem personally gave to the Kohanim for honor and glory. 1
Seforno: It means that Hashem handed the Levi'im to the Kohanim as a gift, to perform any task in the Mishkan that they ask them to.
Ramban: As the Gemara says in Sotah, 15a, commenting on Pasuk 8 (in connection with eating the Korbanos) "le'Mashchah" - 'for greatness, in the way that royalty eats'.
What was the gist of Hashem's answer to the people's concern? A Zar is still Chayav Misah for coming close, and the Leviyim were already commanded to distance Bnei Yisrael (1:53, 3:9-10, 8:19)?
Rashbam (Pesukim 1-7): In answer to Yisrael's complaint, 1 Hashem forbade them with Misah to enter the Mishkan, 2 then He ordered the Kohanim exclusively to perform the Avodah, thereby ensuring that Yisrael will have no reason to come near.
Moshav Zekenim (28, citing Riva): Above (8:19) it says "v'Lo Yihyeh Bahem Negef." This implies that if even one Yisrael approaches, there will be a plague among all Yisrael. When Korach approached the Avodah, Hashem said "Hibadlu mi'Toch ha'Edah", and Moshe said, 'will You be angry with everyone due to one person?!' (16:21, 22) There is a Pesik between "Kol" and "ha'Karev" 3 (17:28)