Background:When an Israelite become poor and sold himself into slavery, he or a blood relative could redeem them out of slavery. This is explained in Old Testament Law:
Leviticus 25:25-28When the Israelites were exiled to Babylon, they are described as being sold into slavery by God.
If your brother becomes poor, and sells some of his possessions, then his kinsman who is next to him shall come, and redeem that which his brother has sold. If a man has no one to redeem it, and he becomes prosperous and finds sufficient means to redeem it; then let him reckon the years since its sale, and restore the surplus to the man to whom he sold it; and he shall return to his property. But if he isn't able to get it back for himself, then what he has sold shall remain in the hand of him who has bought it until the Year of Jubilee: and in the Jubilee it shall be released, and he shall return to his property.
Isaiah 52:3The Jews waited for the Year of Redemption, which was to take place at the same time as the Day of Vengeance (aka Day of Destruction).
For thus says Yahweh, "You were sold for nothing; and you shall be redeemed without money."
You sell your people for nothing, and have gained nothing from their sale.
Thus says Yahweh, "Where is the bill of your mother's divorce, with which I have put her away? or which of my creditors is it to whom I have sold you? Behold, for your iniquities were you sold, and for your transgressions was your mother put away.
For the day of vengeance was in my heart, and the year of my redemption is come.