What does Galatians 4:30 mean?
Paul has constructed an allegory about the difference between those who trust in following the law to save them, contrasted with those who, by faith, trust in what Christ has done. It is the difference between slavery and freedom.To illustrate this, Paul has shown that Ishmael was born into slavery as the son of Abraham's slave-wife (Genesis 16:1–3). This was the result of human efforts, not faith. As the older son, Ishmael may have felt he was secure enough to become Abraham's primary heir, though technically a slave. Perhaps that's why he mocked baby Isaac on the day of a feast to celebrate his being weaned (Genesis 21:8–9).
Sarah, though, saw it happen. Protective of her son Isaac, born in freedom as a result of God's promise (Genesis 21:1–3), she immediately demanded that Abraham cast both Ishmael and Hagar away from their family. She did not want the son of a slave woman to share any part of the inheritance with her son. Abraham resisted, but God confirmed that he should do what Sarah said (Genesis 21:10–12).
Paul's point is very direct. Those who insisted Christians must follow the law to be truly saved correspond to Ishmael. They were still in slavery to sin, and God had cast them out, in a sense. Now that Christ had come, those who followed the law no longer had any part in the inheritance from Abraham. That inheritance is only for those who trust in Christ alone for the forgiveness of sin and a place in God's family.
Galatians 4:21–31 contains Paul's allegory about Abraham's two wives, and the two sons born through them. Paul sets out to use Scripture to show the difference between being born into slavery, by human effort, as opposed to being born into freedom, by the work of God through the Holy Spirit. Ishmael was born into slavery as Abraham's son, but he was cast out when the child of promise arrived. In a similar way, living under the law became pointless when Christ arrived. Those who trust in Him become children of promise by God's power.
In this chapter, Paul uses three new methods to teach his Galatian readers an important lesson. It is futile to follow the law of Moses in order to be made right before God, since justification comes only by faith in Christ. First, Paul shows that the arrival of Christ made it possible for all people to become God's children through faith in Him. Next, Paul makes a more personal appeal, asking what has changed to cause the Galatians to turn on Paul's teaching of the gospel. Finally, Paul builds an allegory from Scripture, illustrating the difference between being born into slavery and being born into the promise by faith in Christ.