Matthew 5:22 But I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, Raca, shall be in danger of the council: but whosoever shall say, Thou fool, shall be in danger of hell fire. Why is the person who calls another a 'fool' in danger of the fire of hell? Is it unjustified anger? Is it the severity of the remark? It is quetioning the persons salvation? The word 'foolish' is used many times in scripture. Raca: Vain fellow Thou Fool: The New Testament. There are fewer Greek terms employed for the fool and these are essentially negative, indicating that the fool is lacking in sense and intelligence. The gravity of the condition of the fool can be seen in the warning of Jesus that to call a person such is to be in danger of "the fire of hell" (Matt 5:22). The designation "fool" is considerably more derogatory than other terms of abuse. Clearly, to be a fool in this biblical sense is a serious matter. http://bible1.crosswalk.com/Dictionaries/BakersEvangelicalDictionary/bed.cgi?number=T269 Matthew 7:26 But everyone who hears these words of Mine and doesn't act on them will be like a foolish man who built his house on the sand. From same link as above: ~~~~~~~~~~~~~~~~~~~~~~~~~~ Paul makes frequent ironic reference to foolishness, particularly in 1 and 2 Corinthians. He deprecates the wisdom of the world, which characterizes God's action in Jesus as nonsensical and scandalous. Human understanding erroneously takes God's wisdom to be foolishness and God's strength to be weakness since God's actions do not fit human reason or expectation. Indeed, from a worldly perspective God uses the foolish thing and calls the foolish person (1 Cor 1:27-28). Paul characterizes his self-defense in 2 Corinthians as foolish. He is forced by circumstances to employ worldly methods of refutation of charges arraigned against him (2 Cor 11:1-6). He is forced to fight fire with fire. Further he recognizes that he is considered a fool by the world because of his suffering for the gospel (1 Cor 4:10). Elsewhere in the New Testament foolish has a more conventional sense. Believers are urged not to be foolish (Eph 5:15-16) and to distinguish carefully between heavenly and earthly wisdom (Jas 3:13-18). This negative attitude toward foolishness is understandable when its practices are observed. Among these practices are: relying on earthly wealth (Luke 12:20); failing to recognize that the ministry of Jesus is God's visitation to claim his own bride (Matt 25:1-13); turning away from the gospel of grace to legalism (Gal 3:1-3); worshiping the creature rather than the Creator (Rom 1:18-23); and abrogating the demands of God with meaningless distinctions (Matt 23:16-22). Perhaps even more significant than the above characteristics is a failure to act on the words of Jesus by building a house without an adequate foundation (Matt 7:26-27), and a failure to believe the good news of Jesus' resurrection (Luke 24:25 — here the foolish are described as "slow of heart" the Old Testament expression is "without heart, " without understanding, as in Prov 9:16). The believer is not to be foolish, but to "understand what the Lord's will is" (Eph 5:17).