When is Acharis ha'Yamim, and why is it discussed here?
Rashi (Yeshayah 2:2): It is after Posh'im will be eradicated. 1
Radak: It is the days of Mashi'ach. This is consolation after mentioning the Churban of Tziyon and Yerushalayim. Malbim - "Tziyon Sadeh Secharesh" (3:12) will be until then. Then it will be rebuilt, via us casting off our evil deeds ? "Kol ha'Amim Yelechu Ish b'Shem Elokav va'Anachnu Nelech b'Shem Hashem" (5).
Radak: This consolation appears also in Yeshayah 2:2-4 with minor differences (because two Nevi'im do not prophesized in the same style ? Malbim).
What is "Har Beis Hashem"?
Rashi (Yeshayah 2:2): It is Har ha'Moriyah (Har ha'Bayis), on which the Beis ha'Mikdash was built. Radak ? after saying that it will be Bamos Ya'ar, it tells that a time will come when it will be at the head of the mountains.
What is "Nachon b'Rosh he'Harim v'Nisa"?
Rashi (Yeshayah 2:2): On the mountain that is the Rosh (head) of all mountains in importance.
Radak: It does not mean that it will be physically higher than it was. Rather, the nations will honor it, elevate it and go there to serve Hashem. He mentions mountains and hills, for the Goyim used to serve their gods on tall mountains. This mountain will be elevated and honored more than all of them.
Why does it say "v'Nisa mi'Geva'os"?
Refer to Yeshayah 2:2:5:1-2.
What is the meaning of "v'Naharu"?
Rashi: They will gather together like Naharos (rivers), which go to the sea.
Radak: They will run. From this, a place where much water runs quickly is called Nahar.
Malbim: Even though it is very high, amidst great desire they will be drawn to it like a river naturally flows to a low place.
