Because of the hardness of your hearts, Moses gave you a way out. The Pharisees approach Jesus with a trick question about divorce. They have heard him teach and they know that if he stays true to his teaching, he will contradict Moses. Now no rabbi in his right mind would want to contradict Moses. Moses is the embodiment of the law. He is THE law! But Jesus is smart. They have Moses on their side, but Jesus has even a greater figure on his side: God! Yes, Moses prescribed for divorce, but what did God actually say? “What God has joined, let no human person, even Moses, separate. Moses did what he did because of your stubbornness.” 
Most, if not all, of humanity’s sins result from stubbornness/hardness of heart (knowing what is right but insisting on the wrong). The human heart has become hardened by a life steeped in sin. Humanity’s salvation lies on the re-constitution of the heart. David had already recognized this and begged God to create in him a new, cleaner heart (cf. Psalm 51). Indeed, the re-constitution of humanity’s heart was central to the making of a new covenant between God and humanity (cf. Ezekiel 36:26), a soft heart in place of a hard one (cf. Ezekiel 11:19), a heart that is sympathetic because it can feel pain. God’s promise of a new heart is fulfilled in Jesus Christ. Jesus appears on the scene and in place of indifference shows sympathy and compassion (cf. the story of the woman caught in adultery). It was a heart that could be pierced with a lance (cf. John 19:34).