Rashi: Kohanim are from Shevet Levi. Radak, Malbim ? this refers to Kohanim who did not stray. They will return to Avodah in the future.

Rashi: He was the Kohen Gadol who served in the Mikdash in the days of Shlomo ? therefore they are called on his name.

Refer to 40:46:3:1-2.

Rashi: When they strayed.

Mishnas R. Aharon 4, p.21: There is a special reward for guarding Mishmeres Hashem when others slacken. Shevet Levi merited their reward also in the world to come for not participating in the Egel ? just the contrary, they answered Moshe's call "Mi la'Shem Elai" (Shemos 32:26).