Why does it say "lemi'Ymei"?
Radak: The prefix Lamed Mem is like l'Mah, leme'Rachok, leme'Olam. A long time passed that you did not guard My Chukim - you and your fathers. Therefore I did evil to them and to you.
Malbim: He begins to rebuke them about Terumah and Ma'aser. You already veered from My Chukim from the days of your fathers.
What do we learn from "Shuvu Elai v'Ashuvah Aleichem"?
Malbim: Due to the sin of [not giving] Terumah and Ma'aser, rain is withheld. The laws of Shamayim depend on these Chukim. When you veered from My Chukim of Terumah and Ma'aser, I removed the Chukim of rain and produce. If you will return to Me, I will return to bring down to you rain and Brachah.
What is the question "how will we return"?
