Reward her — This God speaks to the executioners of his vengeance. Even as she hath rewarded — Others; in particular, the saints of God. And give her double — This, according to the Hebrew idiom, implies only a full retaliation.
Related Commentaries of Revelation 18:6
Revelation 18:6
6 Reward her even as she rewarded you, and double unto her double according to her works: in the cup which she hath filled fill to her double.