God said to Moshe: "Look, I have made you a god to Pharaoh, and Aharon your brother will be your prophet." (7:1)
This line is easier to understand if you remember that in Egypt, Pharaohs were considered to be gods. To Pharaoh, being a god did not mean living in heaven and doing miracles. Pharaoh undoubtedly performed religious charades to exemplify his supposed godliness, but from a practical point of view, the main consequence of being a "god" was that he had temporal power over other humans. Now Moshe, through the plagues, was going to take Pharaoh's temporal authority away from him. Moshe of course was not technically a god. But he would soon become a "god to Pharaoh", lording it over Pharaoh the way Pharaoh had previously lorded over the Egyptians.