What does Exodus 4:21 mean?

God said to Moses, 'When you get back to Egypt, do all the miracles I’ve given you the power to do in front of Pharaoh. But I’m going to make Pharaoh stubborn, so he won’t let the people go.' Exodus 4:21 - Modern Text Bible

(God tells Moses to perform miracles, but warns him that Pharaoh will resist because God will harden his heart.)