In this passage, Paul draws from the story of Sarah and Hagar to make a powerful point about spiritual freedom and inheritance. Hagar, the slave woman, and her son Ishmael represent the old covenant, which is based on the law and human effort. In contrast, Sarah, the free woman, and her son Isaac symbolize the new covenant, characterized by grace and divine promise. Paul is urging the Galatians to reject the bondage of the law, which cannot bring true spiritual inheritance, and instead embrace the freedom and promise that come through faith in Christ.
This allegory emphasizes the transition from the old to the new covenant, highlighting that believers are not bound by the law but are free to live as children of God, heirs to His promises. It's a call to live in the liberty that Christ provides, leaving behind the constraints of legalism. By doing so, believers can fully participate in the blessings and inheritance that come from being part of God's family, enjoying the spiritual freedom that is their birthright through faith.