'Harden' in the Bible

Then the LORD told Moses, "When you set out to return to Egypt, keep in mind all the wonders that I've put in your power, so that you may do them before Pharaoh. But I'll harden his heart so that he won't let the people go.

I'll harden Pharaoh's heart and I'll add more and more of my signs and wonders in the land of Egypt.

Why should you harden your hearts just as the Egyptians and Pharaoh hardened their hearts? Isn't it true that after God toyed with them, they let Israel go, and off they went?

Why, LORD, do you make us wander from your ways and harden our hearts, so that we do not fear you? Turn back for the sake of your servants, for the sake of the tribes that are your heritage.