But the LORD hardened Pharaoh’s heart: this is identical to the words in 10.20 and 9.12, using the verb meaning to make strong. The meaning is simply that Yahweh “made the king stubborn” (Good News Translation). (See the discussion at 4.21 and 7.13.)

And he would not let them go is literally “and he did not agree to let them go.” This is the first time the word meaning “to consent,” or “to be willing,” has been used in reference to the Pharaoh. New Revised Standard Version has “he was unwilling.”

Quoted with permission from Osborn, Noel D. and Hatton, Howard A. A Handbook on Exodus. (UBS Helps for Translators). New York: UBS, 1999. For this and other handbooks for translators see here .