By using the sixth commandment as His first reference point, Jesus began teaching His disciples God’s expectations for them, while at the same time also exposing the hypocrisy of the scribes and Pharisees.
You have heard that the ancients were told, “You shall not commit murder” and “Whoever commits murder shall be liable to the court.” But I say to you that everyone who is angry with his brother shall be guilty before the court; and whoever shall say to his brother, “Raca,” shall be guilty before the supreme court; and whoever shall say, “You fool,” shall be guilty enough to go into the fiery hell (Matt. 5:21-22).
First, note that Jesus was warning about something that could cause a person to go to hell. That was His primary theme—Only the holy will inherit God’s kingdom.
The scribes and Pharisees preached against murder, citing the sixth commandment, apparently warning that murder could land one in court.
Jesus, however, wanted his disciples to know what the scribes and Pharisees didn’t seem to realize—there were much “lesser” infractions that could land one in court, apparently God’s court. Because it is so important that we love one another (the second greatest commandment), when we become angry with a brother we should consider ourselves already found guilty in God’s court. If we verbalize our anger by speaking in an unkind way to him, our infraction is even more serious, and we should consider ourselves guilty in God’s highest court. And if we go beyond that, spewing out hatred for a brother with a second slur, we are guilty enough before God to be cast into hell! That is serious!
Our relationship with God is gauged by our relationship with our brothers. If we hate a brother, that reveals that we do not possess eternal life. John wrote,
Everyone who hates his brother is a murderer; and you know that no murderer has eternal life abiding in him (1 John 3:15).
If someone says, “I love God,” and hates his brother, he is a liar; for the one who does not love his brother whom he has seen, cannot love God whom he has not seen (1 John 4:20).
How important it is that we love each other and, as Jesus commanded, work for reconciliation when we are offended at one another (see Matt. 18:15-17).
If therefore you are presenting your offering at the altar, and there remember that your brother has something against you, leave your offering there before the altar, and go your way; first be reconciled to your brother, and then come and present your offering (Matt. 5:23-24).
This is to say that if our relationship with our brother is not right, then our relationship with God is not right. The Pharisees were guilty of majoring on minors and minoring on majors, “straining out the gnat and swallowing the camel” as Jesus said (Matt. 23:23-24). They stressed the importance of tithing and giving offerings, but neglected what was much more important, the second greatest commandment, to love one another. How hypocritical it is to bring an offering, supposedly to show one’s love for God, while violating His second most important commandment! This is what Jesus was warning against.
Still on the subject of the strictness of God’s court, Jesus continued:
Make friends quickly with your opponent at law while you are with him on the way, in order that your opponent may not deliver you to the judge, and the judge to the officer, and you be thrown into prison. Truly I say to you, you shall not come out of there, until you have paid up the last cent (Matt. 5:25-26).
It is best to stay out of God’s courtroom altogether by living at peace with our brothers as much as is possible. If a brother or sister is angry with us and we stubbornly refuse to work for reconciliation “on the way to court,” that is, on our journey through life to stand before God, we may certainly regret it. What Jesus said here is very similar to His warning regarding any imitation of the unforgiving servant in Matthew 18:23-35. The servant who was forgiven but who refused to forgive had his debt reinstated and he was handed over to the torturers “until he should repay all that was owed” (Matt. 18:34). Here Jesus is likewise warning of the dire eternal consequences of not loving our brother as God expects.
 This applies to our relationships with our brothers and sisters in Christ. Jesus called certain religious leaders fools (see Matt. 23:17), as does Scripture in general (see Prov. 1:7; 13:20).