Who says "Mi Nasan li'Mshisah Yakov"?
Radak (23): Yisrael should confess and say so (but they do not).
Malbim (23): This is the response to their question. Look at the result, and infer the cause!
What is the significance of "Mi Nasan li'Mshisah Yakov"?
Radak: Do not say that it is chance - rather, Hashem did so due to our sins.
Malbim (23-24): This cannot be chance. Surely Hashem did all this! He did not want to eradicate them - He increased Torah to bring merit to them (21)!
What is "Zu Chatanu Lo"?
Rashi: Our sin caused us to be plundered. Radak - it is as if it says Zu Asher Chatanu. Or, Zu is in place of Asher, like "b'Reshes Zu Tamanu" (Tehilim 9:16).
Malbim: In this matter via which Hashem wanted to bring merit to us - added Torah, we sinned, and caused us to be plundered.
Who did not desire His ways?
Rashi: Our fathers.
Radak: We did not. The verse changes from first person (plural) to third person, like "Heyeh Zero'am la'Bekarim Af Yeshu'asenu b'Es Tzarah" (33:2).
Malbim: The hearts of Yisrael.
It already said that they did not desire His ways. Why does it add "v'Lo Sham'u b'Soraso"?
Malbim: They transgressed indifferently. Therefore, the means to bring merit to them caused their ruin. If a master appointed a servant to run his house, and he benefited him, and the servant rebelled, the master is more angry at him than at a servant [that rebelled] who was not elevated. The love and honor is a reason why the master is more angry.