What are "Shefayim"?
Radak: They are high places, like "va'Yelech Shefi" (Bamidbar 23:3).
What are "Neharos"?
Rashi: A heart that understands Torah and Nevu'ah.
Radak, Malbim: Rivers that will come from the high places.
What does "Midbar" refer to?
Rashi: A place that lacked Chachmah of Torah.
Radak: It is a dry desert. Miraculously, Hashem will put water in the mountain, and all the more so in the valley!
Malbim: It is a desert. Miraculously, Hashem will put lakes there.
What is the significance of springs in the valley?
Radak: Miraculously, Hashem will put water in the mountain, and all the more so in the valley!
Malbim: Normally, only springs come from high places, and rivers are only in low places. Hashem will do oppositely - rivers will come from high places, and springs in low places!
What is the significance of water sources in arid places?
Malbim: There cannot be lakes in such places, for the heat of the sun dries them. However, there will be springs and water sources.