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Lit., "to bring evil to your faces". Inasmuch as the face is the most prominent and expressive part of the human body, it is often used as a metonym for one’s whole being; hence, the "evil done to one’s face" is synonymous with "utter disgrace". Most probably, this passage relates to the destruction of the Second Temple and of Jewish statehood by Titus in the year 70 of the Christian era.
The second doom was due to the rejection of the Message of Jesus. "To disfigure your faces" means to destroy any credit or power you may have got: the face shows the personality of the man.
Merivale in his Romans Under the Empire gives a graphic account of the siege and final destruction (ed. 1890, vii. 221-255). The population of Jerusalem was then 200,000. According to the Latin historian Tacitus it was as much as 600,000. There was a famine and there were massacres. There was much fanaticism. The judgment of Merivale is: "They" (the Jews) "were judicially abandoned to their own passions and the punishment which naturally awaited them". (vii. 221).
Titus's destruction of Jerusalem in 70 A.D. was complete. He was a son of the Roman Emperor Vespasian, and at the date of the destruction of Jerusalem, had the title of Caesar as heir to throne. He ruled as Roman Emperor from 79 to 81 A.D.
This is a parenthetical sentence. If anyone follows Allah's Law, the benefit goes to himself: he does not bestow a favour on anyone else. Similarly evil brings its own recompense on the doer of evil.