Parshas Toldos: What’s the Worry?

Welcome to our new "Parsha Pearls" series on the weekly Torah portion. This week, we find Isaac and Rebecca haven't yet had children and are begging in prayer to the Almighty to become parents. Why are they so worried? Isaac's father Abraham received a solid promise from Hashem that Isaac would father the entire Jewish People (Genesis 21:12). Isn't Hashem's promise enough?