Why should they raise a flag in Tziyon?
Rashi: It is to flee to Tziyon. Malbim - this will say, do not go to the fortified cities, which are weak [and will not stand] opposite the enemy. Rather, rush to Tziyon, which is a protected fortification and the Beis Mikdash of the King.
Radak (5-6): They should raise it on the tower of Tziyon, a high place, so they will see it from afar, and flee and gather to the fortified cities.
What is the meaning of "Ha'izu"?
Rashi: Gather. This is like "Shelach Ha'ez" (Shemos 9:19).
Radak: This is fleeing and gathering to the city, like "Shelach Ha'ez" (Shemos 9:19).
Why does it say "mi'Tzafon"?
Radak: Bavel is to the north of Eretz Yisrael.
