en_tn/pro/14/03.md

the mouth of ... the lips of

The mouth and the lips both refer to what a person says. (See: rc://en/ta/man/jit/figs-metonymy)

a rod for his back

The rod with which people will punish the fool by hitting him on his back for his foolish words is a metonym for the words that come out of his mouth. Alternate translation: "words that will cause people to punish him" (See: rc://en/ta/man/jit/figs-metonymy)

the wise

This word is plural. "wise men" or "wise people"

will preserve them

"will keep them from harm" or "will keep them safe"