Awake, awake; put on thy strength, O Zion; put on thy beautiful garments, O Jerusalem, the holy city: for henceforth there shall no more come into thee the uncircumcised and the unclean.
2 Shake thyself from the dust; arise, and sit down, O Jerusalem: loose thyself from the bands of thy neck, O captive daughter of Zion.
This call is specifically to Jerusalem, Zion, the Holy City. God called them to gather their strength, for they were being freed from captivity forever.
It was common in the East for people to wear sackcloth, roughly equivalent to burlap, and to pour ashes over their heads when they were mourning. God says that time has passed, and they are to rise up, get rid of all signs of mourning and defeat.
They were also to remove the chains that were often used when people were taken captive to another land. Chains were placed around their necks and they were linked together in long lines, and so were marched to their fate.
All of that was over, and this time, it was over for good. There would be no more captivity, no more humiliation, no more subjugation. They will turn to God, and God alone, forsaking all idolatry forever.