Rashi: It is a banner - a sign to gather to him and bring the exiles of Yisrael to him for a gift. Malbim - "v'Hevi'u Es Kol Acheichem mi'Kol ha'Goyim Minchah la'Shem" (66:20).

Radak: It is as if Hashem raises a flag to the Goyim to be zealous to come to the place of the miracle. So on that day all the nations will send Yisrael in their lands, to go in honor.

Malbim: The 10 tribes are not scattered. Rather, they are cast off from their place, further than the rivers of Kush. There they are gathered together, like Chazal's tradition.

Malbim: Shevet Yehudah, whom Hashem spread to the four directions.

Malbim (Bi'ur ha'Milos): Asifah is gathering to a special place, e.g. "va'Ye'esof Osam El Mishmar" (Bereishis 42:17). Those who are Nidachim (removed from their place) will be gathered to their place. Kibutz is not to a particular place; it is the opposite of Nefutzos, who are scattered.