Since it is a righteous thing with God to repay affliction to those who afflict you,
God will suffer evil men to persecute His children in this world, knowing they will withstand the test and thus prove their worthiness to be counted as heirs of the kingdom. These evil doers will get their just dues after a while, and such a dealing with them is declared to be a righteous thing. "The verse means that God will deal out punishment to the ones who have been troubling His children" (Zerr, Vol. VI 154).