Whoso mocketh the poor (see Proverbs 14:31, which is nearly identical). He that is glad at calamities shall not be unpunished (Proverbs 11:21; Proverbs 24:17, Proverbs 24:18). The particular calamity primarily intended seems to be that which reduces a person to poverty.
Delight in others' misfortunes, even those of enemies, is a most detestable form of selfishness and malice. Job, testifying to his own integrity, was thankful to think that he was free from this vice (Job 31:29).
The Greeks had a name for it, and called it ἐπιχαιρεκακία, which is used by Aristotle ('Eth. Nic.,' 2.6. 18). The pious author looks for retributive punishment on such spitefulness. The LXX. tries to improve the contrast by resorting a gloss, "He who rejoices at one who perishes shall not go unpunished; but he who hath compassion shall obtain mercy," which is remarkably like Christ's sentence, "Blessed are the merciful: for they shall obtain mercy."