The lips of the wise spread knowledge, but the hearts of fools are not upright.
Once again “the wise” and “fools” are contrasted in Proverbs. Here the focus is how they think and speak.
“The lips of the wise spread knowledge.” They have something good to say and are willing to pass it along to anyone interested. When something’s working well for me it’s so appropriate that I would be willing to share it with others.
“But the hearts of fools are not upright.” “Fools” are not mentally deficient, but morally deficient. And their real problem is not what they do, but how they think. So this verse notes their “hearts…are not upright.”
One of the truths that comes from this wise saying is the connection between words and thoughts. Jesus said it this way — a couple of times: “For the mouth speaks what the heart is full of” (Matthew 12:34; Luke 6:45).