I know that the oldest sources of the Book of Revelation have the Ancient Greek letters as XIS or XIC which translate into the number 616. So how, over time, did that become XES which translates as 666?
I also remember that Revelation is the only book in the bible that promises to punish anyone who tries to intentionally edit it through God's wrath. So are there any edits? I've seen mistranslations and differing interpretations but is there evidence of intentional editing like in the rest of the bible? And could the number 666 actually be an edit?
Edit- After doing some research, I've found that people are actually still debating about which number came first and Irenaeus himself talked about the two differing numbers in the late 2nd century before the oldest scripts of today even existed and he was adamant that 666 came first. At the same time however, Irenaeus was zealously Catholic and had a polemical agenda and the vast majority of texts from that time are modern Catholic and Orthodox views since almost all non-Catholic views of the time had already been destroyed as heresies. I personally still currently think that 616 is the original but I'm not going to give my reasons why. I can only say that it fits a theory that I've come across, a theory that makes a ton of sense but I'm not absolutely certain.
Edit 2- I also found this comment that mentions the theory that it was changed to accommodate for different translations of the name 'Nero Caesar' since Nero was thought by some at the time to be the Antichrist.
The links that have been posted, and the one that OP found, are all relevant, but they do need pulling together.
The short answer is that 616 didn't become 666. Because 616 isn't the original reading. The earliest manuscript of the passage, and the earliest witness to it (which is older), both give the number as 666. 616 was a variant that existed alongside 666, but was never preferred so far as we know. So the question isn't really why one became the other -- which didn't happen -- but rather why both variants exist. First, the textual evidence.
#The variants
The 616 variant was popularised when a documentary came out in 2003 that played up one manuscript, known as P115 (= P. Oxy. 4499), in which the 616 variant is clearly visible. Some unfortunate phrasing has led to a misapprehension that P115 is the oldest witness to the text. That has in turn created the misapprehension that 616 is the 'original' reading. Neither of these is true.
For reference, the two earlier witnesses to the passage, both of which give the number as 666, are
The catch is that the 616 variant quite literally exists alongside the better known reading, in the case of Irenaeus and P115. That is, they give both variants.
The oldest witness, Irenaeus, gives the 666 reading, then comments (tr. Roberts and Rambaut)
I do not know how it is that some have erred following the ordinary mode of speech, and have vitiated the middle number in the name, deducting the amount of fifty from it ....
He's aware of both variants, but doesn't consider the 616 variant to be legitimate. He doesn't explain why: the most likely inference is that he was acquainted with copies of the text that had 666, but had encountered some people who reported it as 616.
P115 also has both variants, and is more telescoped still. I'll give it in Greek as well for maximum clarity.
[... ὁ ἔχων νο]ῦ̣ν ψ̣ηφιϲ̣[ά]-
[τω τὸν ἀριθμὸν τοῦ θηρίου, ἀριθμὸϲ γ]ὰρ ἀν(θρώπ)ου
[ἐϲτίν· καὶ ὁ ἀριθμὸϲ αὐτοῦ χξϛ] ἢ χιϛ. [ ]
[... Let someone who has sen]se calcu[l]-
[ate] the number of the beast, fo]r [it is the number] of a person:
[and its number is 666] or 616. [ ]
The square brackets indicate parts of the papyrus that are missing; the fact that '666' is in one of those parts is not a problem, because the 'or' is clearly visible and there's nothing else it can mean. The Greek text here is not my own supplement, by the way, but the reading text as printed in the first publication of P115, edited by Professor Juan Chapa.
The upshot is that the 616 variant is very early, and existed alongside 666, but there's no reason to think it's the original reading.
#Why 616 and 666?
There is some wiggle-room for alternate interpretations here, but one quite clearly stands out as the leading interpretation.
The core idea is that both figures are based on a practice where you transliterate words into the Hebrew alphabet, then total up the value of the letters according to their value as Hebrew numerals (א is 1, ב is 2, ג is 3, etc.). This form of numerology is part of a bundle of techniques known as gematria, particularly associated with ancient Rabbinic thought.
The idea of transliterating foreign words into the Hebrew alphabet may seem a contortion, but that too is independently attested, notably in the apocalyptic text 3 Baruch chapter 4. That passage for example discusses a 'dragon' with 360 rivers, based on the conversion
δράκων ('dragon') > דרקון drqwn > 360 (the total of the letters of דרקון)
In the case of 666 and 616, these both equate to the Greek word 'beast' using different grammatical inflections:
θήριον ('beast') > תריון trywn > 666
θηρίου ('of the beast') > תריו tryw > 616
So far, no wiggle-room: this is a pretty straightforward explanation of the calculation or psephon being discussed in Revelation 13.
The wiggle-room comes in when we choose an interpretation of what this 'beast' is being equated to. That process is called isopsephy, a similar practice, but particularly associated with 1st century Greek poetry (that is, not originating in Jewish or Christian thought). In isopsephy, the idea is that you take two words or phrases in Greek, where the numerical value of their letters (α = 1, β = 2, γ = 3, etc.) are equal to one another, and treat their equivalence as a pointed social comment.
For example, we have an epigram with the line
νεόψηφον· Νέρων ἰδίαν μητέρα ἀπέκτεινε.
A novel calculation: Nero killed his own mother.
in reference to the emperor Nero (r. 54-68 CE). Here the isopsephy is that his name in Greek, Νέρων ('Nero'), and the phrase ἰδίαν μητέρα ἀπέκτεινε ('killed his own mother') both total up to 1005.
There are a number of other 1st century examples too; this one happens to be handy because it deals with Nero, just as Revelation 13 does. There the isopsephy is
Νέρων Καῖσαρ ('Nero Caesar', Greek) > נרונ קסר Nrwn Qsr > 666
Nero Caesar (Latin) > נרו קסר Nrw Qsr > 616
one using the Greek form of his name, the other using the Latin form. (Notice incidentally that Revelation 13.18 refers to this as a 'calculation' or psephon, just as the Nero epigram does.)
There are competing isopsephies that have been suggested, but Nero is the only one that explains both 666 and 616. He is additionally the strongest candidate for other reasons too: Nero was a boogeyman figure for late 1st century Christians.
You might want to check out the earlier question /r/AskHistorians/comments/3ata56/why_666_for_the_beast_without_a_base10_positional/ where especially /u/talondearg goes into depth on the different aspects of both numbers.
