What does the Bible say about the allegory of Isaac and Ishmael?

In Genesis 21, the story of Abraham, Sarah, and Hagar provides a poignant allegory that Paul expounds upon in Galatians 4. Isaac, the child of promise, represents the covenant of grace instituted by God, whereas Ishmael, born of Hagar, signifies the covenant of works relying on human effort. This contrast highlights that salvation is a supernatural act of God, reflecting His grace rather than human achievement. As Paul notes, those born of the bondwoman are in bondage, while children of the promise, like Isaac, are free and heirs of God's grace.