What is "Sharon"?
Rashi: It is a region in Eretz Yisrael.
Radak: It used to be a pasture "v'Al ha'Bakar ha'Ro'im ba'Sharon" (Divrei ha'Yamim I, 27:29), and so it will be a pasture for flocks 1 .
Malbim: Also in Yirmeyah (33:12), it says that [every city in Yehudah] will be "Neve Ro'im Marbitzim Tzon."
What is "Emek Achur"?
Rashi: It is like the words imply (a muddy valley).
Radak: Also it is a place of pasture. It says Achur, for initially it had a derogatory name. That name will not be mentioned any more. It will be called Emek Brachah. Also Hoshe'a said "v'Es Emek Achur l'Fesach Tikvah" (2:17).
Malbim: It is called so due to its Charavos (ruins).
Will the cattle merely crouch there?
Radak: They will also graze. Also, they will crouch serenely, without fear of enemies.
Why does it say "l'Ami Asher Derashuni"?
Radak, Malbim: It is for those who sought Me (Tzadikim), and not for those who abandoned Me.