1)
Why does it say "Shuvu" and "v'Heitivu"?
1.
Malbim: These refer to Lavim and Mitzvos Aseh, respectively.
2)
Why does it say "repent... and do not follow other gods"? Was this their only sin?
1.
Radak: This teaches that idolatry is equated to all the Aveiros.
3)
Why does it say "u'Shvu... El ha'Adamah"?
1.
Radak: It is as if it says Al. Similarly, "El he'Harim Lo Achal" (Yechezkel 18:6) is like Al.
4)
Why does it say "Lo Hitisem" and "v'Lo Shematem"?
1.
Malbim: These refer to Divrei ha'Nevi'im and Divrei Torah, respectively.