The sixth commandment includes a prohibition not just against the final act of murder but against everything that leads up to it. When God gave this commandment, as with all the commandments, he expressed it in terms of the last most obvious stage in the carrying out of sin.
When we are angry without a sufficient cause, many other things are present as well. First, pride – ‘I am so special, I will not forgive this’, or it may be pride in the sense that I am not looking at my own faults. I would not be so hard on the other person if I did. Or it may be envy which is wanting to find fault. People will use an unequal balance, and judge others far more severely than they would judge the same thing in themselves. It may be lack of love. All that I have is the result of God’s love towards me, but I don’t have love for other people; certainly no constructive kindness. I make no effort to heal the rift between myself and another. I don’t care that it is an offence to God, and grieves the Spirit. I have taken much from God but I will not do this. That is why we should be so horrified at anger.
Can the word ‘fool’ ever be used? Yes, Christ uses it in Matthew 23:17 of the Pharisees. The point is here again, ‘without a cause’. Christ reserved it for the worst of hypocrites. Unfortunately we all do many foolish things, and people rightly say, ‘You fool, what have you done?’ We do not immediately go to law about it, but we examine ourselves to see what truth there is in it.