As thou didst rejoice at the inheritance of the house of Israel, because it was desolate, so will I do unto thee: thou shalt be desolate, O mount Seir, and all Idumea, even all of it: and they shall know that I am the LORD. So will I do unto thee - Others shall rejoice in thy downfall as thou hast rejoiced at their downfall.
This whole chapter strongly inculcates this maxim: Do as thou wouldst be done by; and what thou wouldst not have done to thee, do not to others. And from it we learn that every man may, in some sort, be said to make his own temporal good or evil; for as he does to others, God will take care to do to him, whether it be evil or good, weal or wo. Would you not be slandered or backbitten? Then do not slander nor backbite. Wouldst thou wish to live in peace? Then do not disturb the peace of others. Be merciful, and thou shalt obtain mercy.
Commentary on the Bible, by Adam Clarke [1831].