1)
Why will they not teach each other?
1.
Radak: It is not because they are at the same level of Chachmah. This cannot be. Ketanim cannot be like Gedolim! Rather, they need not teach the other to know Hashem, i.e. to fear Him, to go in His ways - "ha'Lo Hi ha'Da'as Osi" (22:16; refer to 9:23:3:1, 3). I will give to them a new heart, to know Me.
2)
What sins will Hashem pardon?
1.
Radak: What they sinned when they were in exile.
2.
Malbim: Avon (Mezid) I will pardon. Chet (Shogeg) I will not mention. It will not need pardon!
