Jesus tells us to be very careful how we talk, and what we say. "... and whoever says, 'You fool,' shall be guilty enough to go into the fiery hell" (Matthew 5:22 NAS). So why would Jesus say "You fools" in (Matthew 23:17 NAS). It strikes me that Jesus is not practising what he is preaching! What is your understanding?
"You have heard that it was said to those of old, 'You shall not murder, and whoever murders will be in danger of the judgment.' But I say to you that whoever is angry with his brother without a cause shall be in danger of the judgment. And whoever says to his brother, 'Raca!' shall be in danger of the council. But whoever says, 'You fool!' shall be in danger of hell fire" (Matthew 5:21-22).
The topic is anger without cause. The root cause of all intentional murders is anger (I John 3:15). God had stated, "You shall not hate your brother in your heart. You shall surely rebuke your neighbor, and not bear sin because of him. You shall not take vengeance, nor bear any grudge against the children of your people, but you shall love your neighbor as yourself: I am the LORD" (Leviticus 19:17-18).
A list of three facts concerning anger is given by Jesus:
1. "whoever is angry with his brother without a cause shall be in danger of the judgment"
2. "whoever says to his brother, 'Raca!' shall be in danger of the council"
3. "whoever says, 'You fool!' shall be in danger of hell fire"
Raca, an Aramaic word, means empty-headed. Moros, a Greek word, means dull, sluggish, stupid, or foolish. If you were to translate moros into Aramaic, you would use the word raca. There are people who make detailed arguments between the subtle differences in the shades of meaning between the two words, but the difficulty is that they are comparing words between two different languages which essentially mean the same thing. It would be similar to making an argument based on the difference between the English word "love" and the French word "amour."
A better answer to discovering Jesus' point is look at the Talmud, a record of Jewish traditions. L. Harris in The Inspiration and Canonicity of the Bible states that to a Jew, calling someone a fool in Greek (a foreign language to them) was not fitting, but to call someone a fool in Aramaic (their native language of that time) was a true insult that could be taken to court for a resolution.
Jesus' point is that being angry without cause, whether calling someone a fool in your native language where both understand the insult, or calling someone a fool in a foreign language where one might miss the significance, are all equivalent in the eyes of God. To emphasize this Jesus lists grievances from bad to mild in the view of the Jews, but assigns the consequences in the opposite expected order from mild to very bad. In a sense calling someone a fool in Greek was "worse" because not only was hatred for another being expressed, but that hatred was being disguised or hidden behind the words of another language.
Hatred is not a matter that can be ignored. A person cannot rightly worship God while holding a grudge against a brother. Instead of harboring anger, problems between two people need to be straightened out as quickly as possible. Unresolved problems can quickly grow out of proportion and become major issues that are difficult to bring to an end.
"Woe to you, blind guides, who say, 'Whoever swears by the temple, it is nothing; but whoever swears by the gold of the temple, he is obliged to perform it.' Fools and blind! For which is greater, the gold or the temple that sanctifies the gold?" (Matthew 23:16-17).
Here Jesus is not speaking without cause. The Jews' games with terms of a vow were wrong. But Jesus' words are also not spoken out of anger. This is an accurate judgment of the type of behavior these people were involved in.
It isn't wrong to state that an action was dumb, foolish or other terms to express the fact that someone acted without thinking.
"The fool has said in his heart, "There is no God." They are corrupt, they have done abominable works, there is none who does good" (Psalms 14:1).
"For he sees wise men die; Likewise the fool and the senseless person perish, and leave their wealth to others" (Psalms 49:10).
"Whoever hides hatred has lying lips, and whoever spreads slander is a fool" (Proverbs 10:18).
"The days of punishment have come; The days of recompense have come. Israel knows! The prophet is a fool, The spiritual man is insane, Because of the greatness of your iniquity and great enmity" (Hosea 9:7).
There is a difference between throwing around insults out of anger and accurately labeling bad behavior.