Their united prayer was heard. Yet it was chiefly for the sake of Isaac that God gave them children. It is true, Rebekah's piety equalled her husband's, but the prayer of a pious man who is the son of a pious man is far more efficacious than the prayer of one who, though pious himself, is descended from a godless father.
The prayer wrought a great miracle, for Isaac's physique was such that he could not have been expected to beget children, and equally it was not in the course of nature that Rebekah should bear children.