Why should you tear your hearts, and not your garments?
Rashi #1: I am not adamant that you tear your garments.
Rashi #2: Tear your hearts, and you will not need to tear your garments due to Aveilus.
Radak: If you will tear your hearts, and remove from them all evil thoughts, you will not need to tear your garments, like one who tears due to pain and affliction.
Orchos Tzadikim (Sha'ar ha'Teshuvah DH ha'Shevi'i Tzarich): One needs great invigoration and fences to refrain from what he is used to. He needs a total resolve with all his heart and all his Nefesh to refrain. He will remove the habit from his heart as if he was not accustomed, and habituate himself to despising evil in his heart.
Malbim: Tear your hearts a second time. This is absolute regret over the past. Do not tear your garments due to the evil that comes upon you. Rather, tear your hearts due to your sins, for the sins are worse to you than the evil that befalls you due to them.
The previous verse said "Shuvu Adai." Why is this repeated?
Malbim: After you are close 1 to Hashem (due to the first Teshuvah), repent a second time, amidst love.
Therefore, here it says El Hashem, and not Adai. (PF)
Does "Ki Rachum v'Chanun Hu" give the reason?
Radak: Yes - these are His Midos, like it says in the Torah. He retracts from evil [decreed] against those who repent - "va'Yinachem Hashem Al ha'Ra'ah Asher Diber La'asos l'Amo" (Shemos 32:14).
Malbim: Yes - He will retract the evil, even now that the locusts came and the evil began.
