Wouldn't it have been easier to just let them go on their way right away? Why did He choose to keep hardening Pharaoh's heart?
If you read the story you will find that on the first two instances Pharaoh hardened His own heart.. After two times refusing to obey God.. God then kept Pharaoh's heart hard so that God could perform the miraculous miracles.. God did this i believe to leave the world in no doubt that it was God himself who was freeing the Hebrews from Egypt and that it was not Moses and Aaron..