All the billions that will be left behind are not going to care if they take the mark as they have not Christ found in them and will certainly follow that of the son of perdition for their well being not knowing who they are actually bowing down to as they have made themselves ready for damnation for rejecting Christ.
Sis, as you know, we need to compare Scripture with Scripture to understand what it's saying, so let's begin with Israel, Daniel tells us the AC will make a covenant with Israel that will allow them to rebuild their Temple and begin worship, until the 3 1/2 year mark when he declares to them he is God and demands them to worship him, at this time many Jews will will have their eyes opened and refuse, they are the remnant of Israel that will be saved, however, Rev 7:9, 14 talks about a great number of people that will have washed their robes themselves (through decapitation) and be made righteous, these are those in the false religions and cults that have never heard the true Gospel, how will they hear it, three different ways, i44,000 Jewish evangelists proclaiming the Gospel throughout the world Rev 7:4 an Angel flying around the world preaching the Gospel Rev 14:6, and two witnesses in Jerusalem doing miracles, it says great multitudes from all of the people of the world, so we see many that will trust in Jesus during the Trib.
God does save a remnant out of Israel, not the nation, but the man of God that believe Christ is the true Messiah.
I believe in a Rapture of the Church as us being the Bride of Christ being caught up to meet Him in the Clouds, but also believe we will go through everything of Revelation up to the harvest judgment in chapter 14 right before the vial judgments begin.
Are you basing your belief on the fact that those that are saved are called saints?
1. There are people called saints in the Old Testament.
2. There are people called saints in the Church Age .
3. There are people called saints from the Tribulation.
Remember, the meaning of saint is set aside and that describes each one of these three different time periods.
Here is an interesting observation, the saints of the Church worship God as creator in Chapter 4, in Chapter 5 they worship Him as Redeemer, however we see the Trib saints proclaiming,
Saying with a loud voice, Fear God, and give glory to him; for the hour of his judgment is come: and worship him that made heaven, and earth, and the sea, and the fountains of waters Rev 14:7
Interesting, sounds as if there are the very ones who didn't believe there was a God, that didn't believe in the Creation account and didn't believe in a universal flood....., and that would fit in with them that never heard or understood the Gospel before the Church was Raptured because Jesus tells us if you don't believe what Moses wrote then you won't believe in Jesus or what He has said, ...interesting indeed, guess we will just have to wait and see.