It ought to go without saying that Christians should be characterized by truthfulness, but that’s not strictly what this verse is talking about. Of course, there are other verses which forbid lying in general (such as Ephesians 4:25 and Leviticus 19:11), but this commandment is a bit more specific. God explicitly in this verse forbids us from testifying falsely about our neighbor, especially in a court of law.
Anyone who has seen courts in other nations should be very grateful for the legal system in this country. Little niceties like the presumption of innocence, not being forced to testify against oneself, and the systemic safeguards against police and prosecution abuse are things which we take for granted and which people in other lands would love to have. Of course, any court system other than God’s is going to have some abuse and injustice, but overall it’s one of the best in the world. A lot of that is the product of biblical influence on Western civilization, which filters down into our judicial system.
However, there's one major reform I'd like to put into effect which can be found in Deuteronomy 19:16-21. Read that passage and think about the current penalties for perjury. Just in case you missed it, if you were a false witness in a capital case (in which the accused is subject to the death penalty), then if you're found out you get the penalty he would've gotten if he'd been found guilty. Apparently God takes slandering someone in court much more seriously than we do! Maybe we can’t go as far as this passage would indicate (handing out the death penalty), but I thoroughly believe we need to put some teeth in our perjury laws.
Of course, even outside the courtroom it’s the easiest thing in the world (especially with the internet) to trash someone’s reputation without any repercussions. The book of Proverbs says that “a good name is more desirable than great riches; to be esteemed is better than silver or gold.” In other words, all the silver and gold in the world is not worth as much as being known as a person with good character. As any pastor with any experience can testify, gossip rots out the foundation of any church, and every leader in the church must have a “zero-tolerance” policy on it.
Maybe we don’t commit perjury in an earthly court, but God’s “court” is all around us and always in session. Please remember, in any conversation there’s always at least One other listener.
Lord Jesus, you are Truth in the flesh, and my life should reflect that. May the words of my mouth honor, glorify, and please you.