Why did G-d harden Pharaoh's heart.

Why did G-d harden Pharaoh's heart. We do not no why, but three famous commentators give their opinion's. One of them the Chizkuni says G-d wanted to punish Pharaoh for what he did. So he gave him a strong heart, so he wouldn't die of fear during the ten plagues. Another famous commentator the Ramban says G-d didn't let Pharaoh do teshuva so that he could be punished with the ten plague's. The Seforno says G-d didn't want Pharaoh to do teshuva so that G-d could bring the ten plagues and Bnei Israel could see them and have faith in G-d.


What is your opinion?