This is the essential question, but has gone unanswered throughout this thread. So, let me take a stab at it:
18But someone will say, “You have faith, and I have works.” Show me your faith without [a]your works, and I will show you my faith by [b]my works. 19You believe that there is one God. You do well. Even the demons believe—and tremble! 20But do you want to know, O foolish man, that faith without works is dead?
If you live a sinful life rather than one befitting a person who has been saved by Grace through Faith in Christ, YOU display the Mark Of The Beast. By accepting Jesus as your Savior, you also accept Him as your King and Lord. You obey Him, doing good works as a result. If you show a sinful life, this Mark of The Beast, then perhaps you really do not have true Faith. Good works are not necessary for your Salvation; but, they serve as a Mark of your King.
It’s not as simple as that. While the mark definitely represents the dichotomy of good and evil, it also represents the deceitfulness of the latter and how people can be deluded into thinking they’re living righteously. Knowing what the mark is makes it specific rather than general.