Why did God harden the heart of Pharoah?

"But when Pharoah saw that there was a respite, he hardened his heart and would not listen to them: as the Lord had said," (Ex. 8: 15), "and the Lord hardened the heart of Pharoah, as he did not listen to them; as the Lord had spoken to Moses," (9:12). To the writer of Exodus, both these verses meant the same thing. Whatever happens in history, it is Jehovah who acts. "The Lord will have war with Amalek from generation to generation (17: 16); "and the Lord sent thunder and hail and fire ran down to the earth and the Lord rained hail upon the land" (9: 23). The Hebrews were extremely religious people to whom the Lord God was behind every natural phenomenon. They did not raise the modern question, 'would a good God do evil ?' It is in the face of Jesus Christ that we see God as He is. The O. T. revelation of God was partial and fragmentary (Heb. 1: 1). Our Lord used to point out the sin hidden in the disbelief of hardened hearts (Mb. 6. 52; 8; 17). The Islamic faith in predestination of everything by Allah (kismet) was the faith of the Hebrews in the time of Exodus and so even the hardening of the heart of Pharoah was the doing of God. St. James makes it clear that God does not tempt any one. "Let no one say when he is tempted, 'I am tempted by God'; for God cannot be tempted with evil and he himself tempts no one: but each person is tempted when he is lured and enticed by his own desire." (1: 3) Sin would harden our hearts and we are asked to be vigilant. "Exhort one another everyday, as long as it is called, 'today', that none of you may be hardened by the deceitfulness of sins." (Heb.3: 13) Many such passages like the hardening of the heart of Pharoah in the O. T. then must be interpreted as the faith of that particular time of the writing of that particular book and not as the eternal truth revealed in the N. T. by Jesus Christ, the only Son of God.