Charles Ellicott Commentary Proverbs 25:20

"[As] one that taketh off a garment in cold weather, [and as] vinegar upon soda, So is he that singeth songs to a heavy heart." — Proverbs 25:20 (ASV)

As vinegar upon nitre, by which the nitre is rendered useless.

Is he that singeth songs to an heavy heart—Not the true sympathy advised by St. Paul (Romans 12:15).