Revelation 13:15-18

13:15 The second beast was empowered to give life to the image of the first beast so that it could speak, and could cause all those who did not worship the image of the beast to be killed. 13:16 He also caused everyone (small and great, rich and poor, free and slave) to obtain a mark on their right hand or on their forehead. 13:17 Thus no one was allowed to buy or sell things unless he bore the mark of the beast – that is, his name or his number. 13:18 This calls for wisdom: Let the one who has insight calculate the beast’s number, for it is man’s number, and his number is 666.