Exodus 9:35

And the heart of Pharaoh was hardened,.... Instead of being softened, as it seemed to be when under the plague, it became harder and harder when delivered from it:

neither would he let the children of Israel go; though he had so absolutely promised it, and assured them that he would not keep them, and that they should not stay any longer:

as the Lord had spoken by Moses; that so his heart would be hardened until the signs and wonders were multiplied upon him, God designed to perform, Exodus 4:21.