The magicians may counterfeit, but they cannot countermand

Exodus 7:14-25
Moses and Aaron did just as the Lord had commanded. He raised his staff in the presence of Pharaoh and his officials and struck the water of the Nile, and all the water was changed into blood. 
Pharaoh would not listen to Moses and Aaron, just as the Lord had said.
And all the Egyptians dug along the Nile to get drinking water, because they could not drink the water of the river. Pharaoh did not take even this to heart.
The Nile, heart of the nations economy and worship - its life-blood - turns to blood: the fish cannot live in the chick, red water.
Why?
Moses and Aaron did these judgments in presence of Pharaoh, let Pharaoh know that it is the judgment of the Lord.
Pharaoh was not care his people's living. He didn't care what people drinking.
God knows everything before it is happen, but all of these are under God's sovereignty.
Nine times God acts, and Pharaoh, his magicians and all the gods of Egypt are powerless to reverse God's judgments. The magicians may counterfeit, but they cannot countermand(取消命令，反對命令).
How?
God's judgment is severe than anything in the world. No any one can countermand God's word.