Exodus 11:9
The Lord said to Moses, "Pharaoh will not listen to you, so that my wonders may be multiplied in the land of Egypt."
Exodus 7:3-4
But I will harden Pharaoh's heart, and although I will multiply my signs and my wonders in the land of Egypt,
Exodus 3:19
But I know that the king of Egypt will not let you go, not even under force.
Exodus 10:1
The Lord said to Moses, "Go to Pharaoh, for I have hardened his heart and the heart of his servants, in order to display these signs of mine before him,
Romans 9:16-18
So then, it does not depend on human desire or exertion, but on God who shows mercy.