Why does it say "Mi Yode'a Yashuv v'Nicham"?
Targum Yonasan 1 : One who knows that he has sin, he should repent, and [Hashem] will have mercy on him.
Radak #1: Who knows - perhaps Hashem will retract. Even though we said that among His Midos are to retract from evil, and there is no doubt about this, if there were many sins, He will not retract until He punishes, a little or a lot. Therefore, it says Mi Yode'a.
Radak #2: One who knows the ways of Teshuvah, he should repent, and Hashem will retract from this evil.
Malbim: Even if the Tzibur will not repent, I command individuals - one who knows and understands, he should repent and regret his sins.
Rashi explains very similarly. (PF)
What is the significance of "v'Hish'ir Acharav Brachah"?
Rashi: The locusts 1 will leave over a Brachah afterwards - via Teshuvah, there will be a Brachah in Peros.
Radak: Hashem will leave a Brachah after the locusts. If they will repent Hashem will cast off the locusts, and leave Brachah in vegetation. They will not destroy everything, and the remnant will be for a Brachah.
Malbim: Even though an individual's Teshuvah will not nullify the entire decree, it will leave Brachah. There will remain Minchah and Nesech to Hashem. The evil is according to the multitude of sinners and sins. If one repents, the punishment will be reduced according to his share.
Why did Rashi specify Chasil and Gezem, the last and first species mentioned (1:4)? Perhaps he teaches that the Brachah will come whether they repent at the end of the locusts or at the beginning, or in the middle]. (PF)
What is the significance of "Minchah va'Nesech"?
Radak: From what remains, they will make a Minchah and Nesech - corresponding to "Hachras Minchah va'Nesech mi'Beis Hashem" (1:9).
Malbim: Refer to 2:14:2:3.
