How does God transform from a bullying psychopath in the Old Testament to a loving hippie in the New Testament?

God was seen by the old prophets as fearsome and vengeful, jealous and cruel. When in fact God just wanted to save his people, and be their God. They thought God caused evil to happen as well as good. God can only see and do good, so Jesus came around to explain all this to the Jews, and others. God does allow evil to occur, but he doesn't cause evil. Evil is caused by human beings who follow the wrong god. Good is from people who do the will of God and put his will above their own. It's not that God changed, just the interpretation of the nature of God changed because he was presented in a different way, seen from a different angle.