But Pharaoh hardened his heart is literally “he caused his heart to be heavy.” It means that “the king became stubborn” (Good News Translation). This time also may be translated as “even this time” or “once again” (New English Bible). This is the eighth time in the book that the king’s stubbornness is described in terms of a hard heart, but it only the second time that he is said to have hardened his own heart. (Compare verse 15, and see the comment at 4.21.)

And did not let the people go repeats the same words used in previous references to the Pharaoh’s hard heart. His refusal to let the Israelites go away from Egypt, even for the purpose of offering sacrifices to Yahweh, is always explained as the result of his hard heart.

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 .