"Do ye thus requite the Lord, O foolish people and unwise? is not He thy father that hath bought thee? hath He not made thee, and established thee?" (Deuteronomy 32:6).
This rebuke was by Moses, as he warned the people of God just before their entrance into the Promised Land. It contains the first use of the Hebrew nabal (translated "fool" or "foolish") in the Bible. Here it is applied to God's chosen people after they had been redeemed out of Egyptian slavery by God. This implies that the most foolish of all people are those who have known about God and His great salvation and yet have turned away from His Word.
Paul writes in similar scathing terms of those who had known of God's great deliverance of their fathers from the evil world before the Flood, and yet then abandoned Him for idolatry. "When they knew God, . . . their foolish heart was darkened. Professing themselves to be wise, they became fools" (Romans 1:21-22).
David used the same word about those who decide they can explain things without God, just as do so many intellectuals in modern America. "The fool hath said in his heart, There is no God. . . . Have the workers of iniquity no knowledge? who eat up my people as they eat bread: they have not called upon God" (Psalm 53:1,4).
Even prophets and preachers can become fools if they follow their own wisdom instead of God's Word. "Thus saith the Lord God; Woe unto the foolish prophets, that follow their own spirit, and have seen nothing!" (Ezekiel 13:3).
Jesus similarly rebuked even those He dearly loved, because they were surprised and discouraged when He was crucified. "O fools," He said, because they had been "slow of heart to believe all that the prophets have spoken" (Luke 24:25). God help us to maintain believing hearts, not foolish hearts, as we serve Him! HMM