The concept of ransom or redemption was familiar to both Gentiles and Jews at the time Paul wrote this letter. In everyday life, redemption took a person from a state of slavery upon the payment of a price into a state of freedom.
There are also Old Testament backgrounds to the concept of redemption – mainly the goel or kinsman-redeemer. In Israel it was the duty of the goel to redeem land and possessions that was lost by a relative; we see this situation in the story of Ruth where Boaz had to purchase Naomi’s territory. The context here in Ephesians includes the idea of inheritance, so it is likely that Paul is depicting Jesus as the kinsman redeemer of his people.
Another Old Testament example is the deliverance of the children of Israel from Egypt by the blood of the Passover lamb. The Israelites were slaves to the Egyptians under Pharaoh, but were delivered by a sacrifice as well as by God’s power.
The benefit of redemption that Paul mentions is the forgiveness of sins. This is not a reference to inward deliverance from sin but refers to the new standing that each believer has in the sight of God, which we also know as justification.
Paul tells us here that that the price of redemption was the ‘blood of Christ’. This is obviously a reference to his death as a payment of a penalty, a costly sacrifice. We are aware that Jesus bore the judgment of God against sin. Peter, in 2 Peter 1:19, tells us that the blood of Jesus is precious because it was the blood of a holy and perfect Saviour who died on our behalf, and therefore saves us. The writer to the Hebrews says that the blood of Christ purges the consciences of believers from sinful actions and enables them to serve God (9:14). Paul in Ephesians 2:13 tells us that the blood of Christ makes us secure because through it we are brought near to God. In Hebrews 10:19 we are given access to the presence of God by the blood of Jesus. And John, in 1 John 1:9, tells that through the blood of Jesus we are cleansed from our sins.
It was the sacrificial death of Jesus that liberated believers from the prison in which their sins had placed them.