After Israel returns from their captivity, they need to be restored. Isaiah 52:8 tells us that the reigning of God is to restore Zion by Jehovah.
Then, verse 9 says that the reigning of Israel's God is to comfort His people and to redeem Jerusalem by Jehovah. To redeem Jerusalem here is to deliver Jerusalem out of any kind of trouble, any kind of oppression, and any kind of tyranny.
Verse 10 says that the reigning of God is the salvation of Jehovah's holy arm. This salvation is the salvation of Christ as the holy arm of Jehovah.
In verse 11 Jehovah charged Israel to depart from Babylon. God was redeeming Israel out of Babylon; hence, they needed to depart. God provided a way for the Jews to depart from Babylon, yet many were not willing to depart. According to prophecy, a good number of Jews will be left in foreign countries because they are not willing to depart.
In verse 12 Jehovah said that He will go before the departing and returning ones and will be their rear guard, just as the Angel of Jehovah did for Israel in the exodus from Egypt.