What does Proverbs 10:9 mean?

This proverb is like a modern English expression. Attributed to Mark Twain, it says, "if you tell the truth, you don't have to remember anything." An honest, sincere life doesn't run the risk of being caught in lies or deceit. The honest person, therefore, has a more "secure" life. No one can legitimately build a valid case against him.

However, Solomon also points out that the person who conducts himself dishonestly and commits evil will be discovered, eventually. Not long before Twain, Walter Scott noted, "Oh, what a tangled web we weave, when first we practise to deceive!" Trying to keep multiple lines of lies from tangling with each other is a losing effort. Eventually, liars are exposed.

Christians ought to heed Solomon's words and lead such a life that no one can legitimately find fault with them. When the apostles instructed the believers in the early church at Jerusalem to select seven men to oversee the welfare program, they said, "Pick out from among you seven men of good repute, full of the Spirit and of wisdom, whom we will appoint to this duty" (Acts 6:3). But such integrity is also supposed to characterize the life of every Christian. Paul admonishes the Philippian believers: "Do all things without grumbling or disputing, that you may be blameless and innocent, children of God without blemish in the midst of a crooked and twisted generation, among whom you shine as lights in the world" (Philippians 2:14–15).