Quick answer
Perjury is assault with three weapons. The verse refuses to treat lying about someone as a speech problem.
Read both lines
Three weapons, and they are not interchangeable. A club is crushing and close, a sword is cutting and still within reach, an arrow travels and strikes a man who never saw who fired it. Read as a sequence they describe increasing distance, which is exactly what false testimony achieves: the liar does his damage without being in the room when it lands.
The book has spent whole runs on false witness, at 19:5 and 19:9 and 21:28, and it usually speaks about consequence. Here it speaks about the victim, and the shift matters. The offense is not that the liar will get caught. It is that a person is being struck.
Related: Proverbs 19:5 · Proverbs 19:9 · Proverbs 21:28 · Proverbs 12:18
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.