In Deuteronomy 29, Moses recaps some of Israel's history:
And Moses called unto all Israel, and said unto them, Ye have seen all that the LORD did before your eyes in the land of Egypt unto Pharaoh, and unto all his servants, and unto all his land; The great temptations which thine eyes have seen, the signs, and those great miracles: Yet the LORD hath not given you an heart to perceive, and eyes to see, and ears to hear, unto this day. (Deuteronomy 29:2-4)
At first glance, the last sentence seems a little strange, but The Dake Annotated Reference Bible clears it up for us, on page 237 of the Old Testament:
On the surface this verse suggests that God was responsible for the people not having proper faculties, but it literally means they didn't use their faculties properly and the grace He gave them that they might know Him better. Therefore, they were not wise, loving, and obedient as they should be. Had they had eyes eager to see, ears eager to hear the Word of God, and hearts eager to obey it, they would have been commended. However, by not using their own created faculties the right way it proved they had grieved God and hardened themselves against the Holy Spirit and the means of grace. God hated this (v. 4; cp. Dt. 5:29). The same complaint was made by Isaiah and quoted in Mt. 13:14-16, which further explains this verse. See Isa. 6:9-10. Pharaoh is an outstanding example of one who, through his refusal to hear and obey, hardened himself when God gave him the opportunity to be broken and obedient. See Harden in the Index.