Did Christ Need to Die? (Galatians 2:20; COD Head 2, RE 7)

We know that our God is a gracious God and a merciful Lord. He is a God who forgives, and so we wonder why does Christ have to die? It would seem logical that God would just forgive Adam and let him return to Eden. However, God does not do this at all, but he sends Christ to die. So, what is the purpose of Christ's death?