What does Proverbs 26:21 mean?

The Hebrew root word translated here as "quarrelsome" is mādon. This refers to strife and division; when describing a person, it means someone prone to fighting or eager to argue. The book of Proverbs advises a careful, calming approach (Proverbs 15:1, 4) instead of looking for an excuse to start a fight. The prior teaching (Proverbs 26:20) noted that gossip and slander—speech associated with a "whisperer" (Proverbs 16:28)—add fuel to disagreements. This was compared to starving a fire of fuel. When improper conversation dies out, so too do many conflicts. In a parallel way, being argumentative can inflame a situation (Proverbs 15:18). Aggression worsens conflict the same way adding wood to a fire makes the blaze grow.

It's possible that Alexander the coppersmith, mentioned in the New Testament, was a "quarrelsome" man. In his closing remarks to Timothy the apostle Paul writes: "Alexander the coppersmith did me great harm; the Lord will repay him according to his deeds. Beware of him yourself, for he strongly opposed our message" (2 Timothy 4:14–15). Jude wrote about those opposed to faith (Jude 1:18; cf. 2 Peter 3:3) by saying they "cause divisions, worldly people, devoid of the Spirit" (Jude 1:19). Diotrephes, too, was known for words that stirred up trouble. The apostle John writes: "So if I come, I will bring up what [Diotrephes] is doing, talking wicked nonsense against us" (3 John 1:10).