The following is from a post by Tim Keller:
I have always found Jesus’ words in Matt 5:21-22 to be shattering. He begins by reminding his listeners that anyone who murders will be judged. But then he gives three case studies of actions that seem far less serious than murder. “I tell you that anyone who is angry with his brother will be subject to judgment. Again, anyone who says to his brother, ‘Raca’ is answerable to the Sanhedrin. But anyone who says, ‘You fool!’ will be in danger of the fire of hell.” To be bitter and angry in your heart toward someone can lead to great evil, so that makes some sense. But the term "raca" means only something like "you air-head!" and the word translated "fool" is likewise not an outrageous or cutting insult. Jesus’ listeners would likely have been smiling as they heard these terms and would have been shocked as he ended the sentence threatening them with hell-fire! What was Jesus’ point? “The deliberate paradox of Jesus’ pronouncement is that ordinary insults may betray an attitude of contempt which God takes extremely seriously.” (R.T. France, The Gospel of Matthew, p. 201)
While I do not go around calling people "fool" I find substitutes. For the most part, I sin this way in the privacy of my mind, which, as Jesus teaches us is no refuge. But I also know the sinful satisfaction of using my words to inflict pain on someone who, in my mind, has harmed me. Certainly there are times when harsh words are appropriate. The prophets, the apostles, and Jesus Himself used harsh words of rebuke when the situation called for it. However, there is a huge difference between rebuking a scoffer and using words to inflict pain as an end in itself.
It is for the later that I must repent. It is for the later that I must keep a constant watch over my heart and tongue.
All leaders, and especially Christian leaders, must be on guard against this inevitable temptation and this terrible sin. It is natural, when under criticism, to shield your heart from pain by belittling the critics in your mind. “You stupid idiots.” Even if you don’t speak outwardly to people like Moses did, you do so inwardly. That will lead to self-absorption, self-pity, maybe even delusions of grandeur, but the great sin is that the growth of inner disdain leads to pride and a loss of humble reliance on God’s grace. Moses treated God with contempt when he became contemptuous toward his people.
This is what leaders face. Is there any hope for us? Yes, because we are in a better position than Moses was for understanding the grace of God. Don Carson writes: “In light of 1 Corinthians 10:4, which shows Christ to be the antitype of the rock, it is hard to resist the conclusion that the reason God had insisted the rock be struck in Exodus 17:1–7, and forbids it here, is that he perceives a wonderful opportunity to make a symbol-laden point: the ultimate Rock, from whom life-giving streams flow, is struck once, and no more.”