The “Beast” of Revelation has nothing to do with The “Antichrists” (plural) mentioned in the letters of John. The word “antichrist” appears four times in the NT, all of them in the letters of John. Here they are:
**1 John 2:18 Dear children, this is the last hour; and as you have heard that the antichrist is coming, even now many antichrists have come. This is how we know it is the last hour.
1 John 2:22 Who is the liar? It is the man who denies that Jesus is the Christ. Such a man is the antichrist–he denies the Father and the Son.
1 John 4:3 but every spirit that does not acknowledge Jesus is not from God. This is the spirit of the antichrist, which you have heard is coming and even now is already in the world.
2 John 1:7 Many deceivers, who do not acknowledge Jesus Christ as coming in the flesh, have gone out into the world. Any such person is the deceiver and the antichrist.**
“Antichrists” was a term that John coined for any opponents or enemies of Christianity. In particular, he was referring to “false” teachers who were teaching heretical brands of Christianity. He was using the term descriptively and generically. It was not intended to denpote a supernatural entity and it had no relationship to the “Beast” of Revelation.
The Beast was just a coded reference to the Emperor of Rome. Apocalyptic literature was a heavily coded and allegorical way of communicating messages to fellow believers in such a way that the enemy (i.e. the Romans) would not understand it. All of Revelation is about the Roman empire, and the promise that God will take revenge on that empire.
Revelation was conflated with the “antichrist” references in 1 and 2 John, along with the Jewish apcalyptic book of Daniel (which used the 5th Babylonian exile as a metaphor to discuss the 2nd century Maccaeban revolt against Antiochus.) by the Millenielist movement only in the last 100 years or so. The whole Damien/Late Great Planet Earth thing is a relatively new development in Christianity, and is (like the Rapture) pretty much confined to a certain segment of American Christians. Revelation was never interpreted as a prediction of future events (except for the very ending, the bit about final judgement) before the 1800’s and is still not interpreted that way by most Christian churches. The millenialist interpretation has taken such a firm root in American popular culture, though, that many people have no idea how contrived it is.
BTW, here is the Ecclesiastes quotation in context:
18 I also thought, “As for men, God tests them so that they may see that they are like the animals. 19 Man’s fate is like that of the animals; the same fate awaits them both: As one dies, so dies the other. All have the same breath [2] ; man has no advantage over the animal. Everything is meaningless. 20 All go to the same place; all come from dust, and to dust all return. 21 Who knows if the spirit of man rises upward and if the spirit of the animal [3] goes down into the earth?”
22 So I saw that there is nothing better for a man than to enjoy his work, because that is his lot. For who can bring him to see what will happen after him?
As you can see it has nothing to do with either the Beast of Revelation or with John’s Antchrist. It’s a literal reference to animals. There is nothing at all in the Hebrew Bible about either Christ or an Antichrist.