Even though it's only mentioned in Revelation, 666 just might be the most famous number in the whole Bible. Yep, it even gets more play than seven. But what does it mean? And why are people so freaked out by it?
Basically, the number 666 is associated with the Earth Beast, which means it's not good. John says:
[The Earth Beast] causes all, both small and great, both rich and poor, both free and slave, to be marked on the right hand or the forehead, so that no one can buy or sell who does not have the mark, that is, the name of the beast or the number of its name. This calls for wisdom: let anyone with understanding calculate the number of the beast, for it is the number of a person. Its number is six hundred sixty-six. (13:16-18)
So, do we have the understanding to crack the code? Let's find out.
Probably the most popular way of interpreting the "code" behind the number is to pick a word and convert it to numbers. This works with Hebrew since all the letters have a numeric value. For example, the letters in the name "Nero Caesar" happen to total 666.
Interesting, right? Yeah, but it actually turns out that lots of names have a value of 666. Muhammad, Martin Luther, various Popes, Napoleon, Hitler, Mussolini—the list goes on and on. In fact, almost anyone's name can be made to equal 666 if you work with it long enough and in the right language (source).
So while it's probably more likely that John was taking a stab at a specific Roman person or emperor (who was probably someone he saw as a real meanie), we have no way of knowing exactly who that person was. Sorry, secret code, you are lost to the ages.
Here's yet another thought about this scary number: six is one less than seven. Seven is clearly the best possible number (it's all lovely and complete and godly), so six is obviously falling short of that. 666 is like the perfect trifecta of evil. No word on what we're supposed to think of eight. To us, it just seems like he's gone overboard.
Some scholars think that, since John loves picking on Rome (to be fair, they kind of like picking on him, too), and since lacking the mark of the Beast makes it impossible to buy or sell anything, John could also be referring to Roman money. After all, everyone needs to use money. Except Romans coins had an imprint of the emperor's face on them and often bore an inscription declaring him a god. That, boys and girls, is idolatry.
If Christians refused to use the money, stamped with the mark of the Beast, they would be completely left out of the economic system, and life would be pretty hard for them. They would also stick out like sore thumbs, which would make it more likely that someone would start to get suspicious of their activities. What kind of red-blooded Roman doesn't like money?
So it's fair to say Christians might not have been huge fans of Roman coins.
666 has come to symbolize everything bad, evil, and awful. It isn't just the numeric value of the name of some long-dead Roman guy or some wording from a coin. It's come to stand in for the Devil himself. Satan. The Anti-Christ. The Big Bad.
So much so that people often try to avoid the number. Ronald and Nancy Reagan changed the address of their house from 666 to 668 when they moved in. A Dutch Christian organization skipped over the number 666 in their songbooks, so people wouldn't freak out. In the movie The Omen, the demonic little boy has the birthmark of the Beast—a 666 right on his precious little head. Kindergarten is going to be rough.