What should they gird?
Radak: They should gird sackcloth. Malbim - this is for the sake of Tefilah.
Over what should they mourn?
Malbim: The affliction.
What do we learn from "Linu va'Sakim"?
Radak: They should come to Beis Hashem, eulogize, and not remove their sackcloth even at night - perhaps Hashem will have mercy.
Malbim: The Tzadikim ["Mesharesei Elokai"] will pray and repent to overturn the decree.
Why does it say "Mesharesei Mizbe'ach" and "Mesharesei Elokai"?
Radak: Service is like a Mizbe'ach to Elokim. Service (Mesharesei) of Elokim is put Samuch to the Mizbe'ach... 1
Malbim: There were two groups of Kohanim. (a) There were Tzadikim, Mesharesei Hashem, who serve Him with proper intent. They will gird sackcloth and pray. (b) They are "Mesharesei Mizbe'ach"; they offer Korbanos, but not with the proper intent. They will wail like one who despairs, for their Tefilah is not proper.
Surely our text of Radak is mistaken. It cites "Asher Yesharesu la'Shem Bahem"; there is no such verse. Perhaps it should say "Asher Yesharesu Alav Bahem" (Bamidbar 4:14); "Alav" refer to the Mizbe'ach. (PF)
Is "Nimna... Minchah va'Nasech" the only reason to lament?
Malbim: It is why Kohanim should mourn more than the rest of the nation. The locusts ruined the wheat and wine.
