Where do you get this (1-5) —Scripture? I mean, it sounds great, but how do you trust it?
The mark of the beast:
1) It is in the forehead (symbolising thought) or the hand (symbolising deeds)
Firstly, Revelation is a book full of symbolism, so, to take most of it literally would be to misunderstand it completely (as many do). Most of these symbols were previously used in the OT (e.g. in Daniel and a few other books), so the concepts are known from there.
In Ez. chapters 8 and 9 we see an example of "forehead" being used to signify people's thoughts. Daniel is given a vision of God's people committing abominable evil; but, those who sighed and cried at the abominations (i.e. hated them and were deeply moved against them) were to be given a mark in their foreheads (in the vision, not literally) and the judgment would not come upon them.
Ez. 9:4-6 (KJV)
4 And the LORD said unto him, Go through the midst of the city, through the midst of Jerusalem, and
set a mark upon the foreheads of the men that sigh and that cry for all the abominations that be done in the midst thereof.
5 And to the others he said in mine hearing, Go ye after him through the city, and smite: let not your eye spare, neither have ye pity:
6
Slay utterly old and young, both maids, and little children, and women: but come not near any man upon whom is the mark; and begin at my sanctuary. Then they began at the ancient men which were before the house.
The hand is often used to symbolise deeds (e.g. whatever your hand finds to do, do it with your might, as to God and not to men). The right hand, in particular, symbolises one's physical strength.
2) A beast, in prophetic language, is a kingdom, or its ruler, as representing that kingdom
This is well known from; for example, Daniel, where beasts are used to symbolise kingdoms (or the rulers, as representing those kingdoms).
Daniel 7: 2-7
2 Daniel spake and said, I saw in my vision by night, and, behold, the four winds of the heaven strove upon the great sea.
3 And four great beasts came up from the sea, diverse one from another.
4 The first was like a lion, and had eagle's wings: I beheld till the wings thereof were plucked, and it was lifted up from the earth, and made stand upon the feet as a man, and a man's heart was given to it.
5 And behold another beast, a second, like to a bear, and it raised up itself on one side, and it had three ribs in the mouth of it between the teeth of it: and they said thus unto it, Arise, devour much flesh.
6 After this I beheld, and lo another, like a leopard, which had upon the back of it four wings of a fowl; the beast had also four heads; and dominion was given to it.
7 After this I saw in the night visions, and behold a fourth beast, dreadful and terrible, and strong exceedingly; and it had great iron teeth: it devoured and brake in pieces, and stamped the residue with the feet of it: and it was diverse from all the beasts that were before it; and it had ten horns.
These are well known to refer to four kingdoms: Babylon, Medo-Persia, Greece and Rome.
3) 666 means "man man man" (six is the number of man); in other words, it symbolises focus on man, as opposed to God
Six represents man (created on the sixth day). Repeating something, in Scripture, emphasises it (often used) and a triple repetition give maximum emphasis.
4) The beast kingdom is the anti-Church (Roman Catholicism) and its ruler is the anti-Christ (the office of Pope). This kingdom of darkness claims supremacy over every kingdom and person on Earth; in fact, the Pope claims all authority in heaven, on earth and under the earth (i.e. man, rather than God, is in charge, in this evil system)
The office of Pope fits all the biblical criteria for the man of sin/son of perdition/anti-Christ (e.g. he sits in the temple of God (the professing church) proclaiming that he is as God; he has changed times and seasons; claims authority over everyone and everything in heaven on earth and under the earth; is full of names of blasphemy (Holy Father, Rector Orbis, Pontifex Maximus, Vicar of Christ), etc.); and Roman Catholicism fits the criteria for the Whore of Babylon (leaders wearing purple and scarlet; drunk with the blood of the saints; full of heresy; extremely rich; pictured as a woman holding out a cup to the nations (official RC image), etc.).
5) The mark (which others can discern, if they are able) consists of ways of thinking and behaving that conform to this anti-Christ system (Roman Catholicism)
We've seen that, in biblical symbolism, the forehead represents thought and the right hand represents strength and deeds, so a mark (something that can be seen) represents what can be observed of the thoughts (probably via what they say) and deeds.
