The original (but now archaic) meaning of “redeem” was to purchase freedom for someone who was a slave, or in prison. The word more commonly used today for such a transaction is “ransom”; but in biblical usage “redeem” still carries its ancient meaning. We were slaves, in bondage to sin, the moral law, and death; but Christ, by being made a curse for us, has redeemed us from the curse of the law (Ga 3:13). The Israelites were redeemed from Egypt ─ we have been rescued from the grip of Satan.
Something of what it means for one person to substitute himself for another is found in the ancient story of Damon and Phintias –
Phintias had been condemned to death for treason by the ruler of Syracuse, Dionysius I (B.C. 432-367). Before the sentence was carried out, Phintias asked permission to return home to settle his affairs and bid farewell to those he loved. The tyrant refused. But then Damon, a close friend of Phintias, stepped forward, and offered himself as a hostage.
Dionysius agreed, so long as it was understood that Damon would himself be executed if Phintias failed to return. Damon accepted the terms, and was sent off to prison. Phintias set sail for his home, and was not seen again until the day of execution had come. Just as Damon was being led out to his death, Phintias finally arrived, breathless from haste. He apologised for his lateness, explaining that his ship had been delayed by pirates, but he was now ready to submit to his punishment.
Dionysius was so moved by this example of selfless love and friendship that he at once granted Phintias his freedom, and begged to become himself a friend to the two men. (Drawn from A Smaller Classical Dictionary, by William Smith, 1882.)
So Jesus proved himself our Friend, except that in his case no one came to his rescue. He had to tread the winepress of heaven’s wrath alone (Is 63:3), all stained with blood, until the work of redemption was done.
Paul uses an uncommon verb in our texts, exagorazo, which means literally “to buy out of slavery”. Christ was driven by love to the cross, by love he held himself there, until he was able to cry, “It is finished!” The price was fully paid. The slaves can shake off their chains. The taskmaster no longer has any authority over them. Let them now learn how to stand fast in the freedom for which Christ has so wonderfully set them free! (Ga 5:1)