The second beast also forced all people, small and great, rich and poor, free and slave, to have a mark put on their right hand or their forehead. No one could buy or sell without this mark. (This mark is the name of the beast or the number of its name.) Anyone who has understanding can find the meaning of the beast’s number. This requires wisdom. This number is the number of a man. It is 666.
Revelation 13:16-18 (ERV)
Then a third angel followed them shouting, “Anyone worshiping the creature from the sea and his statue, and accepting his mark on the forehead or the hand must drink the wine of the anger of God; it is poured out undiluted into God’s cup of wrath. And they will be tormented with fire and burning sulphur in the presence of the holy angeles and The Lamb. The smoke of their torture rises forever and ever, and they will have no relief day or night, for they have worshiped the creature and his statue, and have been tattooed with the code of his name.”
Revelation 14:9-11 (TLB)
Then I saw some thrones and people sitting on them. These were the ones who had been given the power to judge. And I saw the souls of those who had been killed because they were faithful to the truth of Jesus and the message from God. They did not worship the beast or its idol. They did not receive the mark of the beast on their foreheads or on their hands. They came back to life and ruled with Christ for 1000 years.
Revelation 20:4 (ERV)