god hardened pharaohs heart

interesting, i wonder why god would purposefully harden pharaohs heart? god sends moses to free israel, but then tells moses that he will make pharaoh not let israel go free:

And the Lord said unto Moses, When thou goest to return into Egypt, see that thou do all those wonders before Pharaoh, which I have put in thine hand: but I will harden his heart, that he shall not let the people go.

its obvious from this that freeing israel wasnt gods only purpose with moses' visit. its either something personal with ramses, moses or wanting to show miracles, probably a combination of everything.