Jamieson, Fausset and Brown on Obadiah 1:12

12. looked on--with malignant pleasure, and a brutal stare. So the antitypes, Messiah's foes (Psa 22:17). Maurer translates, as the Margin, "thou shouldest not look" any more. English Version agrees with the context better.

the day of thy brother--his day of calamity.

became a stranger--that is, was banished as an alien from his own land. God sends heavy calamities on those who rejoice in the calamities of their enemies (Pr 17:5; 24:17, 18). Contrast the opposite conduct of David and of the divine Son of David in a like case (Psa 35:13-15).

spoken proudly--literally, "made great the mouth"; proudly insulting the fallen (Eze 35:13, Margin; compare 1Sa 2:8; Re 13:6).