Exodus 10:3 - Clarke's commentary and critical notes on the Bible

And Moses and Aaron came in unto Pharaoh, and said unto him, Thus saith the LORD God of the Hebrews, How long wilt thou refuse to humble thyself before me? let my people go, that they may serve me. How long wilt thou refuse to humble thyself - Had it been impossible for Pharaoh, in all the preceding plagues, to have humbled himself and repented can we suppose that God could have addressed him in such language as the preceding? We may rest assured that there was always a time in which he might have relented, and that it was because he hardened his heart at such times that God is said to harden him, i.e., to give him up to his own stubborn and obstinate heart; in consequence of which he refused to let the people go, so that God had a fresh opportunity to work another miracle, for the very gracious purposes mentioned in Exodus 10:2. Had Pharaoh relented before, the same gracious ends would have been accomplished by other means.