Who says "Lechu v'Nashuvah?"?
Rashi: They will say so. Radak ? this was in the days of Yoshiyah, when they sought Hashem and served Him
Why will they say "Lechu v'Nashuvah El Hashem"?
Radak: This is to invigorate themselves, like "Lechu v'Nachshevah Al Yirmeyah" (Yirmeyah 18:18), "Lechah Na Anasekah v'Simchah" (Koheles 2:1) and similar verses. They do not mean going, rather, invigorating. This expression is used, for going is zealous and sitting is lazy.
Malbim: They will say this amidst afflictions.
What is the grammatical form of "Taraf"?
Radak: It is past tense, even though there is a Kamatz under the Tes and Reish. There are many words like this.
Why will they say "Ki Hu Taraf"?
Radak: Since He tore, we should repent to Him.
Malbim: The afflictions were not natural ? they came from Him. If so, only He can heal us. This refers to the internal illness.
What is the meaning of "Yach v'Yachbeshenu"?
Rashi: "Yach" is present tense; He strikes us, "v'Yachbeshenu" (and He will bandage us). Malbim ? this refers to the external wound, which requires a bandage on the break. The salvation depends totally on Him.
Radak: "Yach" is future tense, in place of past tense; it should say Yakeh. He struck, and if we repent, He will heal.