What do we learn from "Hiskosheshu va'Koshu"?
Sanhedrin 18a, 19a: We must say that a Kohen Gadol and a king of Beis David can be judged. If they could not be judged, they could not judge - "Hiskosheshu va'Koshu" - first fix yourself, then correct others! Rashi - this expounds both words like Hekesh - man evens himself and straightens his way.
Rashi: Hiskosheshu - gather together. This is like "Lekoshesh Kash" (Shemos 5:12). Va'Koshu - equate your deeds to your Maker's intent.
Radak: This is seeking matters and gathering them, like "Lekoshesh Kash", "Mekoshesh Etzim" (Bamidbar 15:32). Seek your blemishes, and afterwards seek others' blemishes and eradicate them. The Dagesh in the Shin [in va'Koshu] is in place of the second Shin. This is like "v'Sobu Es ha'Ir" (it should say v'Sovevu).
Malbim: Because he compared them to scattered chaff that the wind carries, he counsels them Hiskosheshu - gather it (they should join to repent).
Why does it say "ha'Goy Lo Nichsaf"?
Rashi citing Targum Yonasan: [The nation] did not desire to return to Torah.
Radak: [The nation] did not desire this, to seek [blemishes and eradicate them]. This is like "Nichsafta l'Veis Avicha" (Bereishis 31:30).
Radak citing his father: This nation is not ashamed of their deeds. We find Ichsif (Bava Basra 111a - ashamed).
Malbim: You are not ashamed to be not pleasing to Hashem. This parallels "Bakeshu Es Hashem Kol Anvei ha'Aretz" (3); here discusses those who are not ashamed from Hashem.
