@FromOffTheStreets
I don't like jumping in the middle of a book and giving meaning to a passage. But, I have found that most "faith alone" denominations, once you're "saved", they start hitting the 666 deal and spouting stuff about headlines of today meaning this and that fulfills that in Revelation.(Ever notice how that has changed so many times over the years?) My oh my stuff, wring your hands, preaching confusion because the preachers don't know what they are talking about, much less their audience.... just like you did. (Forget the passages about salvation, what is 666?)
16-18
The beast(Rome) marked his own people. God marked his people in Chapter 7 to show that they are his, the beast marks his people here. Both reasons are the same, to show they are theirs.
God knows his people. Satan also knows his people. Everyone on earth then and everyone on earth today is wearing someone's mark. Each of us either belongs to God or to Satan. Each of us is either in the power of darkness or "in the kingdom of God's dear son" (Colossians 1:13)
All sorts of distinctions exist. We base them on race, wealth, politics, etc. But, really only one distinction matters. Is one in Christ or out of Christ? That's the distinction. Whose mark were they wearing? Whose are we wearing?
In 17, no one could buy or sell without the mark, which is the name of the beast or the number of his name.
In chapter 2 and 3 you can see the economic persecution the churches were going through from the trade guilds in Rome. They required you to confess Caesar as Lord to buy, sell or trade. You were no patriot of Rome if you didn't and you suffered hardship because of it. They were faced with a daily choice, Caesar or Christ.
18 Remember, keep your figurative language glasses on. That means what is written many times represents something else.
Revelation is an apocalypse. The writings are characterized by imagery, symbols and signs.
Briefly, (I'm supposed to give you the meaning without any background, or leading up to "the" verse of all time to many)
In chap 13, John saw two beasts (one coming up out of the sea, v. 1, and the other coming up out of the earth, v. 11); both are allies of Satan. Keeping with the symbolic use of numbers "six" represents that which is evil. Tripled it would be intensified evil. Being short of the number seven (a symbol of perfection), the number 666 also shows failure or doom.
"The number of the beast stands for the complete and total failure of all human systems and efforts antagonistic to God and His Christ"- Homer Hailey, Gospel Preacher