For as you in time past were disobedient to God, but now have obtained mercy by their disobedience, even so these also have now been disobedient, that by the mercy shown to you they may also obtain mercy. For God has shut up all to disobedience, that he might have mercy on all.
One of the arguments expressed against Christianity is that if God were good, why would He ever allow evil to exist in the world? First of all, I want to make it very clear that God does not need to answer that question at all. He defines morality so the question itself is absurd. We should simply study Him and understand what good is. That being said, I believe that God is a God of reason and He wants us to understand something about evil here.
Remember that it was disobedience that brought sin into our world. God gave Adam and Eve one requirement and they broke it. I think that we all know that we would have done the same based on the choices we have freely made in our lives. We are a part of the evil in this world and like them, our evil is realized in our disobedience. Evil and disobedience go hand-in-hand and God gives a reason here for why He allows disobedience in our world.
God tells us that He “has shut up all to disobedience, that He might have mercy” on all of us. It’s good to to realize that you can’t know mercy unless you deserve punishment. This is not a justification for disobedience, it is an explanation for why God allowed it to exist. By shutting “up all to disobedience,” God simply set up the conditions that allow us to understand what His mercy is like.
This means that we, of all creatures that He has made, know what God’s love through mercy is. So, one of God’s reasons for allowing evil, is to show His love to us in a unique way. We also read that God has set up the situation so that both the Jews and the Gentiles would be able to experience this same thing. God is a God of love so it only makes sense that a significant reason why evil exists in the world is because He wants to show His love to us.