1)
Why does it say "Ki"?
1.
Rashi: See that Hashem will do judgment against Resha'im, and be humbled and repent!
2)
Why does it say "Chalah v'Necheratzah"? Verse 22 already "Kilayon Charutz"?
1.
Radak: The repetition teaches that the eradication will be total. I will eradicate, and it will be absolute.
2.
Malbim: Even though Hashem decreed eradication [against Yisrael], and after the final decree, it must come, he will put another in place of them - Nochrim who anger Hashem. Am Hashem will be saved.
