Many Christians believe the 666 mark will be a biochip implant to create the cashless society of Revelation 13.
Why is it so bad?
All who take the mark will be damned by God to be cast into the Lake of Fire.
Why will those who take the mark be damned?
I think it’s because God made Silver and Gold as honest weights and measures to be used as money!
Money is NOT paper (which is a promise), not electronic credits, not chips, not a mark, nor a number!
For more, see:
The Use of Paper Money Violates All of the Ten Commandments
Here are the main verses on 666, the mark of the beast:
Revelation 13:16 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:
Revelation 13:17 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.
Revelation 13:18 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. (666)
Using the extended meanings of the original Greek text, Michael E. O’Brien created an alternate possible translation given of Rev. 13, that indicates a biochip implant containing a number like the social security number could fulfill the prophecy very precisely: Rev 13:  He [the second beast] caused everyone, small and great, rich and poor, free and slave, to receive an etching of servitude (made with a sharp point) in their right hand, or in their foreheads;  so that no one could buy or sell unless they had the etching of servitude, or the authority of the beast, or the number of his authority.  Here is wisdom. Let him that has understanding count the pebbles as the number of the beast, for it is an individual’s [identification] number. His number is incised with a pricking action – willingly – by one claiming to possess the Godhead…
In the USA, 98-99% of all transactions are already cashless, and cash represents about 1-4% of bank deposits. (See my article, “Major Frauds of the U.S. Monetary System“. Smart cards and biochip pet implants are in wide use in Europe. Many Christians strongly suspect that this “mark of the beast” prophesy will be implemented by technology that exists today, the biochip implant (syringe implantable microchip/lithium transponder), or an invisible tatoo designed to go in the right hand or forehead.
So, when will the mark of the beast come?
The technology exists today, and people are getting chips implanted under their skin today.
We have the social security number today, we have paper money today.
But I believe the final and ultimate fulfillment of the prophecy of the mark of the beast will take place in the second half of the 7 year tribulation, and before that, Christians may escape that time of trouble in the rapture.
Bibleprophesy.org — teaching the pretribulation rapture, that I believe will come before the time of the mark of the beast.
Here are more scriptures in Revelation that talk about the mark of the beast. Note, in Revelation 19:20, the people who take the mark are deceived! This means they are tricked, or that they do not know the full implications of what they are doing. The may not realize that taking the mark is an act of worship, or that it is an evil action that God hates.
Revelation 14:9 And the third angel followed them, saying with a loud voice, If any man worship the beast and his image, and receive his mark in his forehead, or in his hand,Revelation 14:10 The same shall drink of the wine of the wrath of God, which is poured out without mixture into the cup of his indignation; and he shall be tormented with fire and brimstone in the presence of the holy angels, and in the presence of the Lamb:Revelation 14:11 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.Revelation 14:12 Here is the patience of the saints: here are they that keep the commandments of God, and the faith of Jesus.
Revelation 15:2 And I saw as it were a sea of glass mingled with fire: and them that had gotten the victory over the beast, and over his image, and over his mark, and over the number of his name, stand on the sea of glass, having the harps of God.
Revelation 16:2 And the first went, and poured out his vial upon the earth; and there fell a noisome and grievous sore upon the men which had the mark of the beast, and upon them which worshipped his image.
Revelation 19:20 And the beast was taken, and with him the false prophet that wrought miracles before him, with which he deceived them that had received the mark of the beast, and them that worshipped his image. These both were cast alive into a lake of fire burning with brimstone.
Revelation 20:4 And I saw thrones, and they sat upon them, and judgment was given unto them: 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.Revelation 20:5 But the rest of the dead lived not again until the thousand years were finished. This is the first resurrection.Revelation 20:6 Blessed and holy is he that hath part in the first resurrection: on such the second death hath no power, but they shall be priests of God and of Christ, and shall reign with him a thousand years.
The move to a cashless system is not a war against cash. It is really a war against gold and silver. Paper money cash has already served it’s useful purpose, to get people to forget that gold and silver are money. Cash and bonds are used to take the gold and silver away from the people.
In sum here are my prophetic views: I believe the rapture will happen before the seven year tribulation. I believe the mark of the beast will start half way through the seven year tribulation, when the Antichrist sits in the temple in Jerusalem, and demands to be worshiped as God. I believe the war of Ezekiel 38 takes place at the start of the tribulation, which will look like Armageddon. Israel is wealthy in gold and silver and cattle, and is at peace, before this war. I believe that in order for the prophecy of Ezekiel 38 to take place, the world will have to return to a world gold standard, and I believe it is likely that there will be a world government, perhaps for an entire generation before the rapture. I believe that the Great Harlot of Revelation 17-18 is the international bankers, or perhaps a few hundred families of Jerusalem, who were prophesied to lend to the nations which helps them rule over them. The harlot is destroyed by the seventh beast which is a world kingdom with ten kings, and they give their power to the eighth beast, the Antichrist, who installs his mark of the beast economic system. His system will be against gold and silver, and he will likely use bio-chipping technology to implement the mark of the beast. But the mark is also a number. And remember, those who take it are supporting and worshiping the beast (governmental) system of fraudulent weights and measures instead of God’s system of honest measures, such as gold and silver.