Observe the change of expression. Upon several instances before, it is said that Pharaoh hardened his own heart: but here it is said, that the Lord hardened it. When God gives a man up to a judicial blindness such will be the consequence. The most awful state on this side eternity. See those very solemn scriptures, Hosea 4:17; Rom 1:28; 2 Thessalonians 2:11-12.
Related Commentaries of Exodus 9:12
Exodus 9:12
12 And the LORD hardened the heart of Pharaoh, and he hearkened not unto them; as the LORD had spoken unto Moses.