remember The verses in the book of the Apocalypse says
Apoc 13:11 Then I saw another beast come up out of the earth; it had two horns like a lambs but spoke like a dragon.This beast with two horns "like a lamb" but which "spoken like a dragon" is Satan's parody of the lamb.
12 It wielded all the authority of the first beast in its sight and made the earth and its inhabitants worship the first beast, whose mortal wound had been healed.
13 It performed great signs, even making fire come down from heaven to earth in the sight of everyone.
14 It deceived the inhabitants of the earth with the signs it was allowed to perform in the sight of the first beast, telling them to make an image for the beast who had been wounded by the sword and revived.
15 It was then permitted to breathe life into the beasts image, so that the beasts image could speak and [could] have anyone who did not worship it put to death.
16 It forced all the people, small and great, rich and poor, free and slave, to be given a stamped image on their right hands or their foreheads,
17 so that no one could buy or sell except one who had the stamped image of the beasts name or the number that stood for its name.
18 [b]Wisdom is needed here; one who understands can calculate the number of the beast, for it is a number that stands for a person. His number is six hundred and sixty-six.
A key note is the difference between where the beasts arise -- the first beast arises out of the sea - the sea indicates gentile nations.
This parody of the Lamb represents corrupt leaders within Jerusalem. This parody is later identified by John as the "false prophet" in Rev 16:13; 19:20; 20:10)
As the "false prophet" this parody sets itself up against God's prophets in the days leading to 69 AD.
The false religious leaders who led the persecution of the Christ-sect of Jews in the days leading up to the destruction of the temple in 69 AD are indicated here
The mark of the beast is again a parody of the SIGN on the believers as we read in the letter to the Philadelphians -- the SIGN or Tau being the Hebrew letter which looks like a cross - so the sign of the cross as the christians did was the sign of God
The mark of the beast is linked to the number of the beast - as "wisdom is needed here... it stands for a person..." -- to reveal the identity of the beast to the Christians while hiding it from outsiders, St john used Gematria, the rabbinic numering system for names. When the Gematrian numbers of Nero's official name in Hebrew are added together (50 + 200 + 6+50 + 100 + 60 + 200) they total 666. The Christians KNew that 666 is the number of Nero
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Remember back to the Mark of the Lamb alluded to in the 6th letter to the churches, to the Philadelphians - God's mark is mentioned specifically in the sixth seal of the initial vision (7:3). In Heaven God's faithful "servants shall worship Him; they shall see His face, and His name shall be on their foreheads"..22:4
The mark of the beast is Satan's parody of the sign of the cross. The sign on the forehead talks of loyalty and that on the hand of what we do with the loyalty
We see the same in 14:9 "anyone who worships the beast and its image" is shown as "receiving a mark on his forehead or on his hand"
Nero is the human whose symbol is 666, who demanded worship of himself.
This is the only time in history when the Church was persecuted by both the beast (the Roman empire) and the harlot (Jerusalem authorities)
ST John twice pauses to say "here is a call for the endurance and faith of the saints" (13:10, 14:12). The first time, this is following a statement about not being in armed conflict against the beast "if anyone slays with the sword, with the sword must he be slain" (13:10)
The second time is not to have the mark of the beast -- to be clear the admonition agians thte mark of the beast is "do not worship the earthly power of the roman empire - THAT is the mark of the beast