Thou shalt not bear false witness against thy neighbor
It seems on the surface that this commandment has its roots and highest meaning within the judicial system. When called to give testimony in a legal trial, you must tell the truth. No lying allowed. However, the Eighth Commandment also reminds us of what we learned as children: if you can’t say something nice, don’t say anything at all. One’s reputation and honor are of utmost importance and God commands us to help our neighbor maintain his or her good name. It is not godly to speak ill of another, even if what we say is true. Luther reminds us of Jesus’ teaching on what to do if another in some way hurts, sins, or trespasses against us: do it in private. Do not rally the troops to one side or the other. Simply talk to the person one on one and do not tell anyone else what has transpired, even if you are in the right, or if the issue has been resolved. One’s reputation, once lost, is not easily regained. Remember: if they are talking about someone in a negative light in your presence, imagine what they may be saying behind your back.
From Luther’s Small Catechism
Q. What does this mean?
A. We should fear and love God that we may not deceitfully belie, betray, slander, or defame our neighbor, but defend him, [think and] speak well of him, and put the best construction on everything.
Excerpt From Luther’s Large Catechism*
255] Over and above our own body, spouse, and temporal possessions, we have yet another treasure, namely, honor and good report [the illustrious testimony of an upright and unsullied name and reputation], with which we cannot dispense. For it is intolerable to live among men in open shame and general contempt. 256] Therefore God wishes the reputation, good name, and upright character of our neighbor to be taken away or diminished as little as his money and possessions, that every one may stand in his integrity before wife, children, servants, and neighbors. 257] And in the first place, we take the plainest meaning of this commandment according to the words (Thou shalt not bear false witness), as pertaining to the public courts of justice, where a poor innocent man is accused and oppressed by false witnesses in order to be punished in his body, property, or honor.
271] False witness, then, is everything which cannot be properly proved. 272] Therefore, what is not manifest upon sufficient evidence no one shall make public or declare for truth; and, in short, whatever is secret should be allowed to remain secret, or, at any rate, should be secretly reproved, as we shall hear. 273] Therefore, if you encounter an idle tongue which betrays and slanders someone, contradict such a one promptly to his face, that he may blush; thus many a one will hold his tongue who else would bring some poor man into bad repute, from which he would not easily extricate himself. For honor and a good name are easily taken away, but not easily restored.
276] But the true way in this matter would be to observe the order according to the Gospel, Matt. 18:15, where Christ says: If thy brother shall trespass against thee, go and tell him his fault between thee and him alone. Here you have a precious and excellent teaching for governing well the tongue, which is to be carefully observed against this detestable misuse. Let this, then, be your rule, that you do not too readily spread evil concerning your neighbor and slander him to others, but admonish him privately that he may amend [his life]. Likewise, also, if someone report to you what this or that one has done, teach him, too, to go and admonish him personally, if he have seen it himself; but if not, that he hold his tongue.
Large Catechism Text in the public domain. http://bookofconcord.org/lc-3-tencommandments.php