Why did he say "v'Atah Hashem Yadata"?
Malbim: (You know that they do not really repent.) Do not accept their scream like that of one who admits and abandons [his evil way].
Why would we think that Hashem would atone for them?
Malbim: They [appear to] repent. Do not accept it atone for them without punishments.
What is the meaning of "Al Temchi"?
Rashi: [Their sin] should not be erased. There is a Yud at the end, for their sin is feminine. The Yud is extra, like "va'Tizni Sham" (3:6).
Radak: This is like Al Timcheh (do not erase). The Yud is in place of a Hei, like "Tzur Yeladcha Teshi" (Devarim 32:18).
Malbim: Even after their punishment. [their sin] should not be erased. It should be written in front of You for a permanent remembrance.
How will they stumble?
Bava Kama 16b: Even when they give Tzedakah, make them stumble, by presenting them with unworthy recipients, so they will not get reward.
Malbim: Do not merely remove Your Hashgachah. Overtly punishment them via Hashgachah, which is attributed to You!
What should He do at the time of His anger?
Radak: This is like "va'Yichar Api Vahem va'Achalem" (Shemos 32:10; I will finish them off).
Malbim: It should not be like a punishment that comes to atone for sin; that is from mercy. Rather, it should be amidst anger.
