The idea of hardening one's heart is first found with Pharaoh. There are ten places where the hardening is ascribed to God (Ex 4:21; 7:3; 9:12; 10:1, 20, 27; 11:10; 14:4, 8, 17) and ten places where Pharaoh hardened his own heart (Ex 7:13-14, 22; 8:15, 19, 32; 9:7, 34-35; 13:15).

1. Who hardened Pharaoh's heart first?

The Lord said to Moses and Aaron, "When Pharaoh says to you, 'Perform a miracle,' then say to Aaron, 'Take your staff and throw it down before Pharaoh,' and it will become a snake."
So Moses and Aaron went to Pharaoh and did just as the Lord commanded. Aaron threw his staff down in front of Pharaoh and his officials, and it became a snake. Pharaoh then summoned wise men and sorcerers, and the Egyptian magicians also did the same things by their secret arts: Each one threw down his staff and it became a snake. But Aaron's staff swallowed up their staffs. Yet Pharaoh's heart became hard and he would not listen to them, just as the Lord had said. (Ex 7:8-13, NIV)

2. What does it mean that Pharaoh is hardhearted?

Then the Lord said to Moses, "Pharaoh's heart is unyielding; he refuses to let the people go. (Ex 7:14, NIV)

3. Why did God harden the heart of the Pharaoh and his army?

I will harden the hearts of the Egyptians so that they will go in after them. And I will gain glory through Pharaoh and all his army, through his chariots and his horsemen. The Egyptians will know that I am the Lord when I gain glory through Pharaoh, his chariots and his horsemen." (Ex 14:17-18, NIV)

Before the spies lay down for the night, she went up on the roof and said to them, “I know that the Lord has given you this land and that a great fear of you has fallen on us, so that all who live in this country are melting in fear because of you. We have heard how the Lord dried up the water of the Red Sea for you when you came out of Egypt, and what you did to Sihon and Og, the two kings of the Amorites east of the Jordan, whom you completely destroyed. When we heard of it, our hearts melted in fear and everyone's courage failed because of you, for the Lord your God is God in heaven above and on the earth below. (Josh 2:8-11, NIV)

4. Carefully observe the apostle Paul's statement about God's wrath. How might God harden a non-Believer's heart?

For although they knew God, they neither glorified him as God nor gave thanks to him, but their thinking became futile and their foolish hearts were darkened. Although they claimed to be wise, they became fools and exchanged the glory of the immortal God for images made to look like a mortal human being and birds and animals and reptiles.
Therefore God gave them over in the sinful desires of their hearts to sexual impurity for the degrading of their bodies with one another. They exchanged the truth about God for a lie, and worshiped and served created things rather than the Creator—who is forever praised. Amen. (Rom 1:21-25, NIV)

Jesus answered, "The work of God is this: to believe in the one he has sent." (John 6:29, NIV)

5. At the end of human history, how might God might harden a non-Believer's heart? What does the apostle Paul say?

The coming of the lawless one will be in accordance with how Satan works. He will use all sorts of displays of power through signs and wonders that serve the lie, and all the ways that wickedness deceives those who are perishing. They perish because they refused to love the truth and so be saved. For this reason God sends them a powerful delusion so that they will believe the lie and so that all will be condemned who have not believed the truth but have delighted in wickedness. (2 Thes 2:9-11, NIV)

The beast was given a mouth to utter proud words and blasphemies and to exercise its authority for forty-two months. It opened its mouth to blaspheme God, and to slander his name and his dwelling place and those who live in heaven. It was given power to wage war against God's holy people and to conquer them. And it was given authority over every tribe, people, language and nation. All inhabitants of the earth will worship the beast—all whose names have not been written in the Lamb's book of life, the Lamb who was slain from the creation of the world. (Rev 13:5-8, NIV)