Why does it say "Ki Ma'amadam l'Yad Bnei Aharon?"?
'Rashi': This is like "v'Yilavu Alecha vi'Ysharesucha."
Malbim: There were many Avodos. The Leviyim above 30 did not suffice for them. Leviyim below 30 were used for them; singing and guarding gates was only for those 30 and above.
How were they appointed over "Taharas l'Chol Kodesh"?
'Rashi': If the Bayis or its Kelim 1 became Tamei, they must be Metaher it, like we find in the days of Chizkiyah "va'Ykabelu ha'Leviyim Lehotzi l'Nachal Kidron Chutzah; va'Yachelu b'Echad la'Chodesh Lekadesh?" Malbim - there is a Mitzvah to remove Tum'ah found in the Mikdash.
Radak says 'Kol Kodesh' in place of 'the Bayis or its Kelim.' The Bayis itself cannot become Tamei, like anything attached to the ground (Rashi Shabbos 58b)! (PF)
What is "Ma'aseh Avodas Beis ha'Elokim"?
Radak: 'Ma'aseh' has a Segol under the Sin; it is not Samuch to Avodas. They were ready for everything - deed and Avodas Beis Hashem.
