The law of God and the mercy of God are great especially when they're measured in the person of God - Jesus.
Some hard questions are answered in this ancient text: How can a loving God send people to Hell? How can a good God love "Jacob" and hate "Esau"? The answer is that the law of God is magnificently heavy. It isn't so much that people are bad people deserving of Hell but that God is excellent and the breaking of His law demands the justice of His wrath. And so when we measure the law of God in the cross of Jesus we see just how extravagant God's mercy is too. The law of God and the mercy of God are great.