God delights far more in His mercy than in His wrath. So in order to show the priority of His mercy, He must place it against the backdrop of His wrath. How could God’s mercy appear fully as His great mercy unless it was extended to people who were under His wrath and therefore could only ask for mercy? It would be impossible for them to share with God the delight He has in His mercy unless they saw clearly the awfulness of the almighty wrath from which His mercy delivers them.