I figured since I have written about pools and stools, I might as well say something about fools. Jesus warned not to call someone a fool for whosoever did would be in danger of hell fire (Matt. 5:22). And yet, the word appears at least a hundred times in the Old and New Testaments. The Greek word translated "fool" in this verse is moros which means "a rebel." It has the sense of one sitting in judgment as though they were God, knowing the motives of another person's actions. Rebellion is considered equal to witchcraft and idolatry in the Scriptures (1 Sam. 15:23). For all practical purposes, calling a person a rebel is equivalent to condemning him to hell. Jesus basically is saying be careful how you judge others because you will be subject to the same judgment. Jesus called the Pharisees and the scribes fools, but then He is God and knows how He will judge them in the future (Matt. 23:13-39).
There are numerous other Hebrew and Greek words translated as "fools, foolish, foolishness," but none of them have the same meaning as moros. They should be interpreted as "ignorant" (unlearned), "unwise," "arrogant," and "silly." One who is ignorant is not really expected to know something he has not been taught. However, if he had the opportunity to learn and simply chose to ignore it, then he is foolish. A person is unwise when they misuse the knowledge which they possess. Someone is arrogant when they believe their own understanding of something is superior to the Word, or to wise counsel. Proverbs 12:15 speaks of just such a man, as does Romans 1:22.
Determining what is foolish and what is wise is a very subjective thing. To the Christian, it is unwise to reject God's Word and continue to live a sinful life. Most of us, if not all, have experienced the Hebrews 12:3-15 consequences for our disobedience. Paul said those partaking of the Lord's Supper in an unworthy manner suffered weakness, or sickness, or even death (1 Cor. 11:30).
On the other hand, to the unbeliever, the things of God are viewed as foolish. Moses has prophesied that God would use another "nation" to provoke Israel to jealousy (Rom. 10:19). Yup! The Church is "that nation" (Rom. 11:11). To the world, the preaching of the cross is foolishness (1 Cor. 1:18). To the Greeks (everyone other than Israel), the fact that Christ was crucified is foolishness (1 Cor. 1:23). To the natural or un-regenerated man, the things of the Spirit of God are foolishness (1 Cor. 2:14). God uses the weak to confound the strong (1 Cor. 1:27). It is almost as if everything the world respects, God hates. Everything the world thinks is wise, is foolishness to God. It reminds me of the difference between walking in the flesh and walking in the Spirit; they are total opposites (Rom. 8:1-13). Christians: Fools for Christ!