"Like a club and a sword and a sharp arrow is a man who bears false witness against his neighbor"
Solomon begins a triplet of insights into specific kinds of people with this comparison of violent instruments and the person who would betray someone they know with a lie.
club, sword, arrow
These are instruments of murder. It is interesting to see the type of comparison that Solomon makes. He seems to be interested in making the power of false testimony stand out. It is not harmless; it should not be dismissed by justice; it is not just words. It is designed to do violence to another person. When someone can lie against another, then no one is safe. Unless there is an effective penalty against lying that is actually used, it is possible to murder another person with words and walk away without penalty.
We have a tendency to underestimate the power of lying, and we don't see the way that deception and false testimony aimed against another person can really destroy everything that they have worked for. To lie against someone is serious and should be treated as if that person aimed a sledge hammer at a person or swung a sword at the person or shot an arrow at the other person. These are not just words; they have incredible power to destroy the person.
If you are in a position of authority, don't underestimate the power of words. Stop the bully from destroying a child's psyche. Don't let the person who lies about another get away with it. If you are an employer, make sure that you do not hire a liar even if they can produce good numbers. If you are looking for love, don't connect with a liar no matter how beautiful they are.