In our text Sunday, Paul makes a comparison between Abraham’s two sons. His first son, Ishmael, was the result of a union with Hagar, his concubine, a slave woman. It was Abraham’s way of helping God keep his promise. But Hagar, his concubine couldn’t produce an heir, only a son born in slavery. Paul says that this represents the Jews of his day, enslaved to the law, trying to leverage human effort to secure their salvation.
His second son, Isaac, through his free wife Sarah, was born seventeen years later when he and his wife were unable to conceive. God kept his promise but did it in a way no one could take credit for it. Not only was he born in freedom, but he was born the genuine heir of Abraham’s estate. Isaac represents all who are children of God by grace alone through faith alone.
He concludes that the Gentile Christians were children of promise, and they can’t now rely on human effort to establish right standing with God. So come ready to worship Sunday, for God has set us free in Christ