What do we learn from "Ki Im ha'Leviyim Asher Rachaku"?
Rashi: So you will do to the Leviyim who distanced from Me and became priests [to idolatry], and now they retracted.
Radak (11): "Im" is a Shevu'ah, like "Im l'David Achazev", "Im Yavo'un El Menuchasi" (Tehilim 89:36, 95:11).
What sin will they bear?
Rashi: They will not approach My Mizbe'ach. Rather, they will be appointed [to be guards] on gates of the Bayis.
Radak (10-11): The Leviyim who distanced from Me ? if they will come to My Bayis, it will not be to offer Korbanos. "Leviyim" refers to Kohanim, who are from Shevet Levi. The Vov in "v'Nas'u" is extra, like the Vov in "va'Yisa Avraham Es Einav" (Bereishis 22:4). What will they do? Refer to 44:11:1:1.