What is the meaning of "Al Har Nishpeh Se'u Nes"?
Rashi: Raise a banner to gather against a mountain that is b'Shofi (serene and confident). Radak - this is like 'the owner consumed [the produce] for three years b'Shofi' (Kesuvos 20a, i.e. without protests).
Radak: "Nishpeh" is elevated and tall, like "va'Yelech Shefi" (Bamidbar 23:3), "u'Se'i Al Shefayam Kinah" (Yirmeyah 7:29).
Radak citing Targum Yonasan: For a great city that sits serene, i.e. Bavel.
Why should they wave the hand?
Rashi: This is for those who are far away, and cannot hear; they will see the waving of the hand, and come.
Radak: Raising a banner and waving the hand are a metaphor; it is as if he calls them to come and raise a banner on a high mountain, and wave the hand for them to come quickly to Bavel to destroy it. Paras and Madai will come.
Why does it say "Pischei"?
Rashi: This is like b'Fischei. "Va'Teshev Beis Aviha" (Bereishis 38:11) means b'Veis Aviha.
Rashi citing Menachem: They are swords. This is like "v'Hemah Pesichos" (Tehilim 55:22) [Radak - and "v'Es Eretz Nimrod bi'Fsacheha" (Michah 5:5)].
Who are "Nedivim"?
Radak #1: They are the officers of Bavel. They were great in wealth and level. Usually, great and renowned people are generous.
Radak #2: They are Paras and Madai. This is like the Perush that "Pischei" are swords (refer to 13:2:3:2).