Reflections on Proverb 11:9

With his mouth the godless man would destroy his neighbor,
but by knowledge the righteous are delivered.
(Proverbs 11:9 ESV)

"Godless" in the Hebrew originally indicated a person who was sacrilegious or profane. Because this kind of activity would have involved going into holy places only to defile them, "godless"-- by the time   this proverb was written-- had developed into the idea of "hypocritical," specifically referring (in this text) to a gossip who pretends friendship but then acts like an enemy in secret.

"Knowledge" does not just refer to being knowledgeable in general, but to knowing how to exercise self-control: refraining from speaking when silence is necessary.