What is "v'Hayah mi'Dei Chodesh b'Chadsho"?
Radak: This is like from month to month; "Dei" shows the constancy of the matter, without interruption.
Why does it add "mi'Dei Shabbos b'Shabato"?
Radak: It mentions short intervals for close places, and longer intervals for far places, e.g. annually or less frequent, based on distance from Yerushalayim.
Malbim: Every month, and every week, new Goyim will bow in front of Me to accept the true Emunah and cast off their idols.
Why does it say "Kol Basar"?
Radak: It refers to all people, and even other nations. This is like "vi'Yvarech Kol Basar Shem Kodsho" (Tehilim 145:21). Everyone left from all the Goyim "v'Alu Midei Shanah v'Shanah Lehishtachavos l'Melech Hashem Tzevakos v'Lachog Es Chag ha'Sukos" (Zecharyah 14:16). It specifies Sukos, for the war of Gog and Magog will be at that time.
