Ability to understand the things of God is the gift of God (compare 1 Corinthians 2:13-14); yet man is not guiltless if he lacks that ability. The people had it not because they had not felt their want of it, nor asked for it. Compare 2 Corinthians 3:14-15.
Related Commentaries of Deuteronomy 29:4
Deuteronomy 29:4
4 Yet the LORD hath not given you an heart to perceive, and eyes to see, and ears to hear, unto this day.