[popsicesHoupe]

The argument I used to believe for "why 666?" is that the number "7" is often used in Scripture as a symbol of completeness and perfection, so "6" would be a falling short of perfection. The Beast, the Antichrist and the false prophet form a kind of "unholy trinity", so this is represented by a trinity of sixes - 666.

That's been supplanted for me by Irenaeus' argument (though the old one may also be true to some degree). He puts it this way in Against Heresies, Book V, Chapter XXX:

Such, then, being the state of the case, and this number being found in all the most approved and ancient copies [of the Apocalypse], and those men who saw John face to face bearing their testimony [to it]; while reason also leads us to conclude that the number of the name of the beast, [if reckoned] according to the Greek mode of calculation by the [value of] the letters contained in it, will amount to six hundred and sixty and six; that is, the number of tens shall be equal to that of the hundreds, and the number of hundreds equal to that of the units (for that number which [expresses] the digit six being adhered to throughout, indicates the recapitulations of that apostasy, taken in its full extent, which occurred at the beginning, during the intermediate periods, and which shall take place at the end) As a side note, while some older manuscripts of the Revelation list the number of the beast as 616, Irenaeus explicitly mentions and rejects that number (on the basis of the testimony of those who spoke personally with John as well as on the testimony of manuscript copies, as stated in the above quote). He cautions that:

For if these men assume one [number], when this [Antichrist] shall come having another, they will be easily led away by him, as supposing him not to be the expected one, who must be guarded against. However, he's not that big on trying to figure out ahead of time who the Antichrist is through numerical calculations. As he says a little farther along:

But, knowing the sure number declared by Scripture, that is, six hundred sixty and six, let them await, in the first place, the division of the kingdom into ten; then, in the next place, when these kings are reigning, and beginning to set their affairs in order, and advance their kingdom, [let them learn] to acknowledge that he who shall come claiming the kingdom for himself, and shall terrify those men of whom we have been speaking, having a name containing the aforesaid number, is truly the abomination of desolation.

... It is therefore more certain, and less hazardous, to await the fulfilment of the prophecy, than to be making surmises, and casting about for any names that may present themselves, inasmuch as many names can be found possessing the number mentioned; and the same question will, after all, remain unsolved.

... for if it were necessary that his name should be distinctly revealed in this present time, it would have been announced by him who beheld the apocalyptic vision. For that was seen no very long time since, but almost in our day, towards the end of Domitian’s reign.

But he indicates the number of the name now, that when this man comes we may avoid him, being aware who he is: the name, however, is suppressed, because it is not worthy of being proclaimed by the Holy Spirit. In Christ,
Mike