Irenaeus of Lyons, Against Heresies, 5.28

In this world some run toward the light and, through faith, join themselves to God, while others turn away from the light and separate themselves from him. The Word of God comes bringing a dwelling suited to everyone: for those who are in the light, that they may enjoy it and the good things within it; for those who are in darkness, that they may share in the calamities that belong to them. Therefore he says that those on the right are called into the kingdom of the Father, but those on the left are sent into eternal fire, because they have deprived themselves of every good (Matt 25:34, 41).

For this reason the Apostle declares: because they did not receive the love of God so as to be saved, God will send them a working of error, so that they believe a lie, so that all who did not believe the truth but consented to iniquity may be judged (2 Thess 2:10-12). When that one comes, he will recapitulate the apostasy in himself by his own sentence, and by his own will and choice he will do whatever he does, and he will sit in the temple of God so that those he deceives may worship him as Christ; therefore they will justly be thrown into the lake of fire (2 Thess 2:4; Rev 19:20). Yet God, according to his providence, foreknows all things and at the fitting time sends the one who is to be such a person, so that they may believe falsehood, so that all who did not believe the truth but consented to iniquity may be judged.

John signified his coming in the Apocalypse: the beast I saw was like a leopard, its feet were like a bear's, and its mouth like a lion's mouth; the dragon gave it his power, his throne, and great authority (Rev 13:1-2). One of its heads seemed to have been slain to death, but its death wound 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, saying, 'Who is like the beast, and who can fight against it?' (Rev 13:3-4). A mouth speaking great things and blasphemies was given to it, and authority to act for forty-two months (Rev 13:5). It opened its mouth to blaspheme God, to blaspheme his name and his dwelling place, and those who dwell in heaven (Rev 13:6). Authority was given it over every tribe, people, language, and nation, and all who dwell on the earth worshiped it—everyone whose name has not been written from the foundation of the world in the book of life of the Lamb who was slain (Rev 13:7-8). If anyone has an ear, let him hear. If anyone is to be taken captive, to captivity he goes; if anyone is to be killed with the sword, with the sword he must be killed. Here is the endurance and faith of the saints (Rev 13:9-10).

Then I saw another beast rising out of the earth, the one he calls the false prophet. It spoke like a dragon and exercised all the authority of the first beast in its presence, and it made the earth and its inhabitants worship the first beast, whose death wound had been healed (Rev 13:11-12). It performs great signs, even making fire come down from heaven to earth before people, and by these signs it deceives the inhabitants of the earth (Rev 13:13-14). No one should think it does these signs by divine power, but by magical operation; it is no wonder, since demons and apostate spirits serve it and through them it performs signs and deceives the earth's inhabitants (Rev 13:14; 16:13-14). It will order an image of the beast to be made, give breath to the image so that it can speak, and cause all who refuse to worship the image to be killed (Rev 13:15). It will also cause a mark to be put on the right hand or forehead of everyone, so that no one can buy or sell unless they have the mark, that is, the name of the beast or the number of its name (Rev 13:16-17). The number is six hundred sixty-six: six times one hundred, plus ten times seven, plus six; this sums up the whole apostasy that has taken place over six thousand years (Rev 13:18).

For as many days as the world was made, so many thousands of years it will be completed. Therefore Scripture says: 'And the heavens and the earth were finished, and all their host. And on the sixth day God finished his work that he had done, and he rested on the seventh day from all his work that he had done' (Gen 2:1-2). This is both a narrative of past things and a prophecy of future things. For the day of the Lord is like a thousand years (Ps 90:4); in six days the things that were made were finished, so it is clear that their completion comes in the sixth thousandth year.

For this reason, at every time the human being, formed at the beginning by the hands of God—that is, by the Son and the Spirit—is made according to the image and likeness of God, casting away the chaff, which are the apostasies, but gathering the wheat into the storehouse, which are those who bear fruit in faith toward God (Matt 3:12). Therefore tribulation is necessary for those who are saved, so that—being in a sense broken, refined, and sprinkled with patience by the Word of God, and kindled—they may become fit for the banquet of the King. As one of ours said, when he was condemned to the beasts for the testimony of God: 'I am the wheat of Christ, and I am ground by the teeth of the beasts, that I may be found the pure bread of God' (Ignatius, Romans 4:1). All things were made for the benefit of humanity; and the snares of the Antichrist, his wickedness, and apostate power were prefigured from the flood onward, and afterward in the persecution of Ananias, Azarias, and Misael (Dan 3).