Word Study: Raca - empty, i.e. a senseless, empty-headed man, good for nothing. A term of reproach used among the Jews in the time of Christ. O empty one, i.e. thou worthless (as a term of utter vilification)
Other terms: numbskull, one who thinks like a donkey, You idiot!
Word Study: fool - (Greek mōros - translates to Moron in English). Foolish, impious (not showing respect or reverence, especially for a god), godless because such a man neglects and despises what relates to salvation.
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.
In vs. 22, three levels of severity are described, each falling short of physical murder, but each sinful and destructive.
If a person nurses a hateful and malicious attitude toward a fellow Jew (“his brother”), he could well be brought up before the local magistrate (“the judgment”).
If his hatred is expressed in words of angry contempt (such as “Raca!”–the equivalent of “You stupid idiot!”) it could be a matter for the Jewish supreme court, called the Sanhedrin (“the council”).
Worse still, the one who calls his brother a “fool” thereby suggests his own unsaved condition, which therefore means he is in serious danger of eternal damnation.