Why did God harden Pharaoh’s heart?

In Romans 9:17-18 Paul tells us that God hardened Pharaoh’s heart in order to declare His might and power in the earth.  It may appear that God didn’t give Pharaoh a choice and a chance to listen and let Israel go peacefully, but God gave him many opportunities.  In Exodus we read that Pharaoh hardened his heart on his own 7 times before God began to harden it.  God gave Pharaoh ample opportunity to do what He asked, but Pharaoh refused to listen.  After the 7th time, God honored Pharaoh’s decision and would not allow him to change his mind until God was finished with him and Egypt.  We all get a choice in following and listening to God and either way we choose God will honor our decision.