Since it is a righteous thing with God to repay affliction to those who afflict you,
Seeing it is a righteous thing with God: The word "righteous" (dikaios) means contextually "approved of God, acceptable to God." Thayer comments here that "it is agreeable to justice" (149-1-1342). "A righteous thing with God" means by the side of God (para theoi) and so from God’s standpoint. This is as near to the idea of absolute right as it is possible to attain (Robertson, Vol. IV 43).