Read Exodus 10.
After seven devastating demonstrations of God's absolute power, Pharaoh still refused to yield himself to the LORD. The cost grew higher each time for him and his nation. Systematically, the false gods of Egypt were being shown for what they were--nothing!
Locusts: The Egyptians even had a god to protect them from the swarms of locusts called Serapia.
Darkness: Amon-Re, Aten, Atum, Horus, Harakhte were worshipped as sun gods; Thoth, the moon god.
Pharaoh hardened his heart against the LORD. John Calvin labeled this "outrageous obstinacy". God will get glory from Pharaoh either way (9:16). At that point, the Lord hardened Pharaoh's heart for three reason: so that the Egyptians would witness "these signs among them and that you may tell in the hearing of your son and of your grandson how I have dealt harshly with the Egyptians and what sins I have done among them, that you may know that I am the LORD." (v.2)
Pharaoh made three serious and deadly mistakes.
1. Pharaoh mistook God's word for the word of a human. (v.7)
Despite all that had taken place, the king still wanted to be in charge. God kept pursuing Pharaoh and patiently increasing the pressure. Yet, Pharaoh saw this as a match of wills; his against Moses. A person who ignores God's word does so at their own peril. "For the word of God is living and active, sharper than any two-edged sword, piercing to the division of soul and of spirit, of joints and of marrow, and discerning the thought and intentions of the heart." (Hebrews 4:12)
2. Pharaoh mistook temporary feelings for eternal actions. (vv.16-17)
This was the second time he did this. Under the pressure of moment, he wanted relief. But his words of "I have sinned" and "forgive my sin" proved empty. They were, perhaps, emotionally sincere but were spiritually false. He had no intentions of surrendering his life to the LORD. Remorse is not repentance. The Apostle Paul preached, "...that they should repent and turn to God, performing deeds in keeping with their repentance." (Acts 26:20)
3. Pharaoh mistook partial obedience for doing God's will. (vv.24-27)
Partial obedience is disobedience. He thought he could negotiate what God had commanded. The truth, promised by the LORD in Genesis 15:13-14, was that the Jews were leaving Egypt to return to their real home. It was to be a total exodus. Partial obedience is evidence that a person is holding back from God for self-serving reasons. Such actions cost Saul his kingship and ultimately his life (1 Samuel 15:10-23).
"For the eyes of the LORD run to and fro throughout the whole earth, to give strong support to those whose heart is blameless toward him." (2 Chronicles 16:9)