Why did God harden Pharaoh's heart?

Question from Keri:

We were studying Exodus when the following question came up in my Bible class:

Why does God harden Pharoah's heart (or so the Bible words it) if he wanted the Israelites to go free? The way that's worded is confusing to the students and me.

Answer from Pastor Bob:

Strange as it sounds to us, nine times in Exodus it says that God hardened Pharaoh's heart (4:21; 7:3; 9:12; 10:1; 10:20; 10:27: 11:10; 14:4; 14:8) and another nine times it says Pharaoh hardened his own heart (7:13-14; 7:22; 8:15; 8:19; 8:32; 9:7: 9:34-35). So Pharaoh was responsible for his own actions, but the Lord was ultimately in control of events. It's like the issue of predestination; man has a free choice, but God already knows what that choice will be, so God can speak of it as predestined because of His foreknowledge. The bottom line is that God knew how Pharaoh would resist, but God was going to have His will done, yet without violating Pharaoh's free will. God's purpose through it all was to bring glory to His name. Notice Exodus 6:7: "Then you will know that I am the Lord your God, who brought you out from under the yoke of the Egyptians."