Hagar represents slavery to human effort based on Mount Sinai (4:24–25). In contrast, Sarah represents freedom in the heavenly Jerusalem, God's ideal city. Abraham’s true children by faith now live under God's rule in Jesus Christ (3:29).
she is our mother: Sarah’s son, Isaac, was freely given all of God's promises apart from the law of Moses. Similarly, Jews and Gentiles who live by faith in Jesus are Sarah’s true children. They receive God's promises to Abraham freely apart from the law (3:26–29; 4:4–7).