Here’s a humbling thought – when God showed Abraham the stars in the sky and said, “Your descendants will be like those,” one of those stars had been lit for me. That was a promise that God made to Abraham, something he had to accept through faith. I am part of that story, as are you, if you have surrendered to Christ.
This humbling thought helps me understand what can seem like a confusing passage of Scripture. In essence, though, Paul is saying that Ishmael was born according to the custom and the law of that day. Abraham had no heirs. Sara was barren. According to the law of the land, Abraham could produce an heir with Hagar.
But the realization of God’s promise didn’t come because Abraham followed some custom of his day. It came because God had made a promise to Abraham, and God is not restricted by any barriers. He gave Abraham and Sara a son through His Grace, and that is our story. We are in Christ because God chose to move in a supernatural way.