Irenaeus of Lyons, Against Heresies, 5.28

In this world some run to the light and, through faith, join themselves to God, while others turn away from the light and cut themselves off from Him. Therefore the Word of God comes, bringing a dwelling fit for everyone: for those who stand in the light, that they may enjoy it and the good things found in it; for those who linger in darkness, that they may share in the calamities that belong to them. That is why He declares that those on the right will be called into the kingdom of the Father, but those on the left will be dispatched into eternal fire, because they have stripped themselves of every good thing.

That is also why the Apostle says: because they refused to welcome the love of God that would have saved them, God will send them a powerful delusion so that they believe the lie, with the result that all who did not believe the truth but gave their consent to wickedness will be condemned. When this man arrives, he will gather up the whole apostasy into himself by his own judgment; he will act entirely by his own will and choice; and he will sit in the temple of God, demanding the worship due to Christ from those he has deceived. Consequently, they will be justly thrown into the lake of fire. Yet God, in His providence, foreknows all things and, at the appointed time, sends this very man so that they may believe falsehood, so that all who refused the truth and embraced iniquity may be judged.

John foretold his coming in the Apocalypse: The beast I saw resembled a leopard, its feet were like a bear's, its mouth like a lion's; the dragon handed over to it his own power, his throne, and great authority. One of its heads appeared to have been mortally wounded, but the death-blow was healed, and the whole earth marveled and followed the beast. They worshiped the dragon because he had given authority to the beast, and they worshiped the beast itself, crying, "Who is like the beast, and who can fight against it?" It was given a mouth that uttered arrogant words and blasphemies, and authority to act for forty-two months. It opened its mouth to blaspheme God -- to slander His name, His dwelling, and those who dwell in heaven. It was granted authority over every tribe, people, language, and nation, and all earth-dwellers whose names are not written in the book of life of the Lamb slain from the foundation of the world worshiped it. If anyone has ears, let him hear. If anyone is destined for captivity, into captivity he goes; if anyone is destined for the sword, by the sword he must die. Here is the endurance and faith of the saints.

Then John speaks of the beast's lieutenant, also called the false prophet: he spoke like a dragon and exercised all the authority of the first beast on its behalf. He compels the earth and its inhabitants to worship the first beast, whose fatal wound had been healed. He performs great signs, even calling fire down from heaven to earth before men's eyes, and by these signs he deceives the earth-dwellers so that they do not suppose he works by divine power but by sorcery. No wonder: demons and apostate spirits serve him, and through them he performs signs that seduce the inhabitants of the earth. He will order an image of the beast to be made, breathe life into it so that it can speak, and put to death all who refuse to worship it. He will cause a mark to be placed on the right hand or forehead of every person, so that no one can buy or sell without the beast's name or the number of its name. That number is six hundred sixty-six -- six times one hundred, plus ten, plus seven, plus six -- summing up the whole apostasy accomplished in six thousand years. For as many days as the world took to make, so many thousands of years it runs.

That is why Scripture says: "The heavens and the earth were finished, and all their host. On the sixth day God finished the work He had done, and He rested on the seventh day from all His work." This account of the past is also a prophecy of the future. A day of the Lord is like a thousand years; in six days creation was finished, so it is clear that the consummation comes in the sixth millennium. Throughout all time, man -- formed at the beginning by the hands of God, that is, by the Son and the Spirit -- is being shaped according to the image and likeness of God. The chaff, which is apostasy, is cast away; the wheat, those who bear fruit in faith toward God, is gathered into the storehouse. Therefore tribulation is necessary for those who are being saved, so that, broken and refined and sprinkled through patience with the Word of God and kindled by it, they may become fit for the King's banquet. As one of our own said when condemned to the beasts for the sake of martyrdom in God: "I am the grain of Christ; I am ground by the teeth of beasts, that I may be found the pure bread of God." All things were made for the benefit of humanity, and the deceits, wickedness, and apostate power of the Antichrist were prefigured from the flood onward, and afterward in the persecution of Ananias, Azarias, and Misael.