This commandment forbids all sins of the tongue [James 3], by which we may injure or confront our neighbor. To bear false witness is nothing else than a work of the tongue. Now, God prohibits whatever is done with the tongue against a fellow man. This applies to false preachers with their doctrine and blasphemy, false judges and witnesses with their verdict, or outside of court by lying and speaking evil. Here belongs the detestable vice of speaking behind a person's back and slandering, to which the devil spurs us on. It is a common that everyone prefers hearing evil more than hearing good about his neighbor. We ourselves are so bad that we cannot allow anyone to say anything bad about us. Yet we cannot bear that the best is spoken about others.
To avoid this vice we should note that no one is allowed publicly to judge and reprove his neighbor—even though he may see him sin—unless he has a command to judge and to reprove. There is a great difference between these two things: judging sin and knowing about sin. You may know about it, but you are not to judge it. I can indeed see and hear that my neighbor sins. But I have no command to report it to others. If I judge and pass sentence, I fall into a sin that is greater than his. But if you know about it, do nothing and cover it until you are appointed to be judge and to punish by virtue of your office. (paragraphs 263-266)
Condensed from CONCORDIA: THE LUTHERAN CONFESSIONS, copyright 2005,2006 by Concordia Publishing House. Used by permission. All rights reserved. To purchase a copy of CONCORDIA, call 800-325-3040.