What three dangers was Jesus warning against at Matthew 5:22?

 
In his Sermon on the Mount, Jesus Christ warned his followers: “I say to you that everyone who continues wrathful with his brother will be accountable to the court of justice; but whoever addresses his brother with an unspeakable word of contempt will be accountable to the Supreme Court; whereas whoever says, ‘You despicable fool!’ will be liable to the fiery Gehenna.”—Matthew 5:22.
 
Jesus used things familiar to the Jews—the court of justice, the Supreme Court, and the fiery Gehenna—to convey to them the increasing severity of the punishments for sins of increasing seriousness.
 
First, Jesus said that everyone who continues wrathful with his brother will be accountable to “the court of justice,” the local court. According to tradition, these courts were set up in cities with an adult male population of 120 or more. (Matthew 10:17; Mark 13:9) The judges at such a court had authority to render judgment, even on murder cases. (Deuteronomy 16:18; 19:12; 21:1, 2) Thus, Jesus was showing that a person who harbors smoldering wrath against his brother is committing a serious sin.
 
Jesus next said that a person who “addresses his brother with an unspeakable word of contempt will be accountable to the Supreme Court.” The Greek word rha‧ka′ (footnote) rendered “an unspeakable word of contempt” means “empty” or “empty-headed.” According to The New Thayer’s Greek-English Lexicon of the New Testament, that word was “a term of reproach used by the Jews in the time of Christ.” Jesus was thus warning against the seriousness of expressing hatred toward a countryman with a derogatory term of contempt. Jesus was as much as saying that a person using such a word would be judged not just by a local court but by the Supreme Court, the full Sanhedrin—the judicial body in Jerusalem made up of the high priest and 70 older men and scribes.—Mark 15:1.
 
Finally, Jesus explained that if a person addresses another, “You despicable fool!” he would be liable to the fiery Gehenna. The word “Gehenna” comes from the Hebrew words geh hin‧nom′, meaning “valley of Hinnom,” which lay to the west and south of ancient Jerusalem. In Jesus’ day, the valley had become a place for burning refuse, including the bodies of vile criminals who were considered undeserving of a decent burial. So the word “Gehenna” was a fitting symbol of complete destruction.
 
What, then, did the expression “despicable fool” signify? The word used here sounded similar to a Hebrew term that means “rebellious,” or “mutinous.” It designates a person as morally worthless, an apostate and a rebel against God. So the person addressing his fellow as a “despicable fool” is as much as saying that his brother should receive a punishment fit for a rebel against God, everlasting destruction. From God’s standpoint, the one uttering such a condemnation against another could merit that severe sentence—everlasting destruction—himself.—Deuteronomy 19:17-19.
 
Consequently, Jesus was setting a higher standard for his followers than that found in the principles behind the Mosaic Law. While people believed that a murderer would be “accountable to the court of justice,” Jesus went further. He taught that his followers should avoid even harboring animosity against their brothers.—Matthew 5:21, 22.