“[He that] speaketh truth sheweth forth righteousness: but a false witness deceit.” (Pr 12:17 AV)
Pretty easy to understand. Lying is deceit. Truth is righteousness. No confusion there. I think Solomon meant something a bit deeper. It is obvious that those who tell the truth are righteous in their words. But what Solomon may be eluding to is a righteousness not limited to the words at hand. Perhaps he means that those prone to tell the truth are also prone to generally live right. Telling the truth is a good barometer into a person’s character. If his habit is to tell the truth, he may have other righteous habits as well. Those who are prone to tell lies usually live a lie. Telling the truth is a foundation upon which a person’s character can be built.
Many years ago, I ran a restaurant. To advance, an employee had to show up a bit early and be ready to clock in when they were scheduled. They could not clock in and then go to the restroom, get their uniform on, and prep themselves to work. They had to be ready when the time to work arrived. I also gave responsibilities to see if they could work unsupervised. It might be prep work or cleaning duties. Checking on them meant I could trust them with more responsibilities. At the end of the night, if work was not done even though the employee said it was, the employee was on notice. Often, we would get a call in and the employee was not sick at all. I remember having to make those phone calls. Thy employee would call in sick and I would wait a few hours. I would call the employee’s home and ask for the person. A parent or sibling would tell me they were at a concert or over at a friend's house. What we found was that if they lied once, they lied more than once. If they were unreliable in small things, they could not be trusted in larger things. Lying about the obscure means they could not be trusted in private.
We teach our children to always tell the truth. We do this because telling the truth is a foundation for character in other areas of life. We teach our children to tell the truth because a liar cannot be trusted with anything. We teach our children to tell the truth because the consequences of lying far outweigh the short-term benefit that lies may produce. I think Solomon is teaching his children a good habit for life. Telling the truth is more important to character development than we may think. A person who is honest with his words will be honest with his behavior. They go hand in hand.