Exodus 4:21
And the LORD said unto Moses, When thou goest to return into Egypt, see that thou do all those wonders before Pharaoh, which I have put in thine hand: but I will harden his heart, that he shall not let the people go. And the LORD said unto Moses, When thou goest to return into Egypt, see that thou do all those wonders before Pharaoh, which I have put in thine hand: but I will harden his heart, that he shall not let the people go.
The words were spoken as part of the commission given to Moses at the burning bush at Horeb, the mountain of God. There God spoke from the flame and called Moses by name. There He declared Himself the God of Abraham, Isaac, and Jacob, the Angel of the covenant who had revealed Himself to the fathers. From there He sent Moses forth as a humble shepherd with only a rod in his hand. That rod God would make the symbol of His power to deliver Israel at the appointed time in a manner to pour contempt on human pride. Moses hid his face because he was afraid to look upon God, showing that humility and reverence characterize all who come into God's presence.
The declaration that God would harden Pharaoh's heart did not mean He supernaturally made Pharaoh rebellious. God hardens Pharaoh's heart by displaying His almighty power and clear evidence before him. When Pharaoh rejects that display, the rejection makes him harder and more firm in rebellion. Hardness of heart increases by continual resistance to God's power, and each rejection deepened Pharaoh's stubbornness.
God in providence preserved Pharaoh and placed him on Egypt's throne at the time of Israel's deliverance. He overrules Pharaoh's hardness and refusal to let the people go so that it magnifies His name. That overruling reveals His power and judgments before the Egyptians and before Israel also.