Exodus 8:15

15Then Pharaoh, seeing that relief had been provided, hardened his own heart, and he did not listen to them, just as the Lord had instructed.
8:15 Pharao hardened his own heart: By this we see that Pharao was himself the efficient cause of his heart being hardened, and not God.--See the same repeated in ver. 32. Pharao hardened his heart at this time also: likewise chap. 9.7, 35, and chap. 13.15.(Challoner)

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