That is a question which is often pondered by many.. Most are confused as to why Jehovah would harden the heart of Pharaoh when He wanted him to let the people go. It would seem at first glance that God was defeating the very thing that He set out to do.
When we read the passages like Exodus 9:12, 10:20, of "The Lord hardened the heart of Pharaoh", it is quite easy to come to erroneous conclusions if we aren't careful. But the truth is, the Lord was not making Pharaoh do evil, the Lord was "allowing" him to do evil.
"For out of the heart proceed evil thoughts, murders, adulteries, fornications, thefts, false witness, blasphemies:"
Only God truly understands the total depravity of man's heart against Him.
"And I will give them one heart, and I will put a new spirit within you; and I will take the stony heart out of their flesh, and will give them an heart of flesh:"
"The Heart is deceitful above all things, and desperately wicked: Who can know it?
I the Lord search the heart, I try the reigns, even to give every man according to his ways, and according to the fruit of his doing." God is releasing His restraint of sin in Pharaoh, that his heart would be in it's normal unreasonable and deceitful state. In this hardening of Pharaoh's heart, the Glory of God will be seen in the signs and wonders for generations to come.
"And I will harden Pharaoh's heart, and multiply my signs and my wonders in the land of Egypt."
The sin of the hardened heart, was truly Pharaoh's.
"But when Pharaoh saw that there was respite, he hardened his heart, and hearkened not unto them; as the LORD had said." Indeed, it was He that made Pharaoh's heart hardened 'by'removing His hand of restraint of his sin. He indirectly hardened it, as this was His judgment and He takes responsibility for this hardening. A judgment upon Pharaoh and a Blessing for generations to come.
While God removed His hand of restraint and hardened the Heart of Pharaoh by this action, the sin is Pharaoh's, not God's. We see this plainly in verses such as,