What is the significance of "Sanu'ach Yad Hashem"?
Rashi: This is His Gevurah.
Radak: His hand will strike the Goyim.
What is the meaning of "v'Nadosh Mo'av Tachtav"?
Rashi: It will be threshed in its place. Nadosh has the same grammatical form as "v'Narotz [ha'Galgal]" - Koheles 12:6].
Malbim: At the end of days, Mo'av and Edom will be under Yisrael - "Edom u'Mo'av Mishlo'ach Yadam" (11:14). Chazal have a tradition that the two kings, Edom and Mo'av, that Yisrael went around their lands when they ascended from Egypt, and Hashem commanded not to fight them, in the future Yisrael will conquer them. Mo'av will come to Har Tziyon to fight Yisrael; Hashem will thresh Mo'av under the mountain, like straw is threshed to make Domen (fertilizer).
How will Mo'av be threshed? The nations were mixed up - nowadays, and also then, it is (was) not known which is Amon, Mo'av, Edom...!
Radak #1: Perhaps some families, it is known which nation they are from.
Radak #2: "Mo'av" refers to those who live in Mo'av (even if they do not descend from Mo'av). The verse mentions Mo'av, for they will help the nations who come from the north to Yerushalayim with Gog and Magog. Since Mo'av are neighbors of Eretz Yisrael and close to them, they will prepare paths for those who come and be with them.
What is "Masben"?
Rashi: It is Teven (straw).
What is "Madmenah"?
Rashi: It is mud. This is like "l'Domen Al Pnei ha'Adamah" (Yirmeyah 8:2).
Radak: It is a waste-heap. Fertilizer in the waste-heap is called Domen.
Radak citing his father: It is a city of Mo'av written in the Nevu'ah of Mo'av - "Gam Madmen Tidomi" (Yirmeyah 48:2). Mo'av will be threshed in its place, i.e. Madmenah, like straw is threshed.
