1)
What is the meaning of "Lenatze'ach"?
1.
'Rashi': It is to supervise. The same applies to "Lenatze'ach Al ha'Melachah" (Ezra 3:8) and "v'Shesh Me'os Menatzchim" (above, 2:17).
2)
Why does it say "Kol Mevin"?
1.
'Rashi': Regarding song 1 , knowledge is called Havanah. Also above, it says "ka'Katon ka'Gadol Mevin Im Talmid", "u'Chenanyahu Sar ha'Leviyim? Ki Mevin Hu"(Divrei ha'Yamim I, 25:8, 15:22).
1
Malbim: I.e. the Chachmah of music. Those who knew were the most esteemed. This is why Chenanyahu was Sar ha'Leviyim. The Leviyim who knew song were appointed over Beis Hashem, for their esteem.
