Why does it say "v'Usaf Shelalchem"?
Rashi: This refers to "ka'Nelosecha Livgod Bagdu Vach" (1). You who betray My nation, when your punishment comes, the remnant of My nation will plunder you. Chazal expounded that this refers to plundering Sancheriv's camp.
Radak: Shelalchem is booty of Goyim that you will gather.
Targum Yonasan: Yisrael will gather the spoils of nations. Radak - if this refers to the days of Mashi'ach, it says also "v'Yatz'u Yoshevei Arei Yisrael u'Va'aru b'Neshek
What is the comparison to gathering of locusts?
Rashi: Your booty will be gathered like the locust gathers grain in the summer - everyone for himself. Also here, everyone will plunder for himself 1 .
Radak: When locusts rest on the ground, people of the city go out and gather them in their Kelim, lest the locusts destroy the grain. So Anshei Yerushalayim will gather the spoils of Machaneh Ashur. It compares the going of the angel in Machaneh Ashur to locusts going on grain - they destroy it.
Radak: When the Navi told Yisrael to gather the spoils, they asked, to divide [among everyone], or everyone for himself? He answered, like locusts.
What is the meaning of "k'Mashak Gevim Shokek Bo"?
Rashi: Like the roar of water that gathers and falls in pits, so will roar those who come to plunder. Mashak is an expression of plundering, like "Ari Nohem v'Dov Shokek" (Mishlei 28:15). Gevim is like "v'Lachsof Mayim mi'Geve" (30:14). 1
Radak: Mashak and Shokek refer to going, like "u'Ven Meshek Beisi" (Bereishis 15:2). Gevim are locusts; the Targum of "Arbeh" (Shemos 10:4) is Guva.
Malbim: When it rains, ponds are full of water, and locusts drown in them. It is easy to gather them. So Machaneh Ashur gathered your wealth.
Radak: When the Navi told Yisrael to gather the spoils of Machaneh Ashur, they said, money of the 10 tribes is mixed in! He answered, "k'Mashak Gevim Shokek Bo" - just like [Tevilah in] ponds raise a person from Tum'ah to Taharah, so Yisrael's money, once it fell in the hands of Nochrim, immediately it is Tahor (permitted).
