What does Proverbs 12:17 mean?

The comment made here seems like a "truism"—a self-affirming or obvious remark—at first. Taken lightly, the English translation seems to say honest people are honest, and liars lie. The context of these phrases, however, involves the kind of "evidence" and "witness" one would expect to see in a courtroom. The word for "truth" here is emu'nāh, implying a person's perception of what is real and actual: a sincere, open conviction. Also, the Hebrew indicates a person who "breathes" truth. The person whose life is marked by natural, innate honesty gives trustworthy testimony (Matthew 5:37). In contrast, the person who habitually lies can't be trusted, no matter what they say. Each witness reveals his character by what he says.

The apostles Peter and John gave truthful evidence about Jesus before the rulers, elders, and scribes. They testified honestly that Jesus is the Messiah who had risen from the dead. When the rulers, elders, and scribes commanded them not to speak or teach in Jesus' name, the apostles answered, "We cannot but speak of what we have seen and heard" (Acts 4:20). Their honest witness showed clearly that they were righteous. On the other hand, the witnesses who had appeared before the chief priests and the Jewish council were deceitful. Matthew 26:59 reports that "the chief priests and the whole council were seeking false testimony against Jesus that they might put him to death." Although many false witnesses showed up, they were disqualified. All these false witnesses demonstrated their unrighteous character.