what is the mark of the beast
The mark of the beast is a number derived from the name of the person Revelation calls 'the Beast'. In Hebrew, letters also represent numbers, so the 'number of a name' in Hebrew was computed simply by adding up the letters (which are also numbers) in the name. This is known as gematria. It's a form of numerology practiced by ancient Jews (and even some modern ones!).
The 'number of the beast' is 666 in modern versions of Revelation, but an ancient fragment has been found that had the number as 616. It turns out that Nero's name added up to 666 whereas Caligula's name added up to 616. Caligula erected a statue of himself in the Temple and demanded he be worshipped as a god (the desecration of desolation referred to in Revelation), so 616 is more consistent with the story.
The general thinking is that the number was originally 616 and stood for Caligula, but when Nero came to power and was even worse than Caligula, they changed it to 666, which then has a double meaning (because 6 is the number of imperfection in Jewish numerology).
"And he causeth all, both small and great, rich and poor, free and bond, to receive a mark in their right hand, or in their foreheads: And that no man might buy or sell, save he that had the mark, or the name of the beast, or the number of his name. Here is wisdom. Let him that hath understanding count the number of the beast: for it is the number of a man; and his number is Six hundred threescore and six" (Rev. 13:16-18).
"And the smoke of their torment ascendeth up for ever and ever: and they have no rest day nor night, who worship the beast and his image, and whosoever receiveth the mark of his name" (Rev. 14:11).
"And I saw the souls of them that were beheaded for the witness of Jesus, and for the word of God, and which had not worshipped the beast, neither his image, neither had received his mark upon their foreheads, or in their hands; and they lived and reigned with Christ a thousand years" (Rev. 20:4).
Yes to all above! (Especially Toadaly.) The book of Revelation was written to encourage persecuted Christians and had to be formulated in a way that they would understand completely but that their persecutors (the aforementioned Roman emperors and their soldiers) would not understand. Thus it uses apocalyptic imagery familiar to Jews from the book of Daniel and other writings, and Jewish numerology, because many of the new Christians in the endangered churches came from a Jewish background.
That's the historical background. Spiritually, I believe that the messages in it are as important for Christians today as they were for the persecuted churches then. Knowing the historical background is necessary if we are going to work out what the complex imagery means for us! It's very easy to get it wrong and get totally messed up ideas...
I don't know any way to say this nice, but Tim LeHay is a theological and historical moron. Please, please, please pay no attention to his cartoonish end times nonsense based on a foolish literal interpretation of the translated texts, rather than a proper symbolic understanding rooted in historical knowledge.
If you want a lot more information - look up Tim Lahaye's prophecy bible. It has everything referenced with notes and descriptions. (He's one of the authors of the Left Behind Series)
I am pretty sure that the ENTIRE book of Revelations is just metaphors, and none of that will really happen in the way described.
The Left Behind series was based on fiction, need I say more...
As always Amblessed, your comments are right on the mark.
666 is the sign of the beast