The metaphors of selling and redeeming link this verse with 50.1-2 (see the comments there).

For thus says the LORD: The Hebrew particle ki rendered For is better translated “Now” or “Indeed,” since it is probably an emphatic marker rather than a logical connector here. Bible en français courant (1997) has “Here indeed.” Good News Translation, Contemporary English Version, Revised English Bible, and New American Bible omit it. Thus says the LORD is the standard divine quote frame (see the comments on 7.7). Good News Translation has “The Sovereign LORD says to his people,” since it combines this quote frame with the next one at the beginning of verse 4. Good News Translation also makes it explicit that God’s people are the addressees.

You were sold for nothing seems illogical since selling something implies receiving money for the thing sold. But as in 50.1, the selling is a metaphor for God sending his people into exile. Sold for nothing means that God was not paid when the Babylonians took them into exile.

And you shall be redeemed without money: Just as God’s people went into exile without the Babylonians paying for them, so God will bring them back without making any payment. In 50.2 God claimed the power to “redeem” his people. Sometimes the Hebrew verb rendered redeemed has the sense of buying back something or some person, often a person sold earlier because of poverty (see the comments on 41.14). This commercial sense is used metaphorically here for God bringing his people back from exile. He will do it without money, that is, without making any payment (see 45.13).

Good News Translation renders the LORD’s words in this verse clearly with “When you became slaves, no money was paid for you; in the same way nothing will be paid to set you free.” Die Bibel im heutigen Deutsch has “When I sold you into slavery, I did not take any money for that. That is why you will be freed now also without any ransom being paid.” For languages that require an active form for the passive verbs were sold and shall be redeemed, translators may specify God as the agent (see the second example below).

For the translation of this verse consider the following examples:

• Now, this is what the LORD says:
“You were sold for nothing,
so you will be brought back for free.”

• Now, this is what the LORD says:
“I sold you and received no payment,
I will bring you back without paying anyone [or, back freely].”

Quoted with permission from Ogden, Graham S. and Sterk, Jan. A Handbook on Isaiah. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here .