Let's follow the threads of narrative.

In Gen 21:12, God signals that Sarah grasps the divine intention in the most vital matter of the covenant—which son would be chosen, the aggressive Ishmael or the non-aggressive Isaac. It is two paths for humanity.

Without God's intervention, Abraham would've chosen Ishmael.

Notice in Gen 27, Isaac does not "listen" to Rebekah in the matter of sons, and chooses the aggressive son, Esau, over her choice, Jacob.