John could have written, “signs by which he deceived many,” or some similar concept. That he mentioned instead those who received the mark
and those who worshiped its image
has specific significance for his readers. With these words John is prompting his readers to recall and re-examine the details of Revelation 13:11–18, and so take note of the fact that this beast had actually succeeded in deceiving people. More, John’s readers lived in a context where they could see with their own eyes that particular acquaintances of theirs had fallen for the beast’s deception; that is, they (like we) knew persons who ended up worshipping the beast. Again, this served to point up the sinister danger of this beast, and so the good news of its capture.
20 And the beast was captured, and with it the false prophet who in its presence had done the signs by which he deceived those who had received the mark of the beast and those who worshiped its image. These two were thrown alive into the lake of fire that burns with sulfur.