The assembly/ the church/ ecclesia refers to the nation of Israel- the 12 tribes/ Gods chosen people who will go through the ( great) tribulation. It's especially for those people for growing/ maturing as we do in this life. If you don't go through tribulation, you don't grow, you dont have any useful life skills to teach anyone. If you stayed in a cabin in the middle of no where your whole life, what good are you to others? How do you show love? Do you even know what love is? And why would Messiah want to marry someone who doesn't show love. We can be grafted into Israel, if we're not from one of the 12 tribes, just as the sojourner was- Gods people who he has covenant with. The bride is going to be a lot smaller than what a lot of believers/ Christians think. Messiah doesn't want a child bride, he wants someone that loves, helps, and is constantly trying to learn about their groom.
The temple in the millennial reign has 12 gates with the name of each tribe written on them. There's no baptist gate, no catholic gate, no muslim gate, no protestant gate, no gentile gate etc. Jesus even tells us he's only come to save the lost sheep of the house of Israel- Matt 15:24
This is my belief- per God's Word, not man's tradition.
There will be a great falling away because billions of people believe they will be raptured away into heaven before tribulation, so once that doesn't happen, because that's what they were taught, their faith will be shaken.
It's going to get a little crazy here before the end of this age folks! If your faith isn't solid, and you don't truly know your Messiah, it will be shaken.
Heres great series to watch on the end times on YouTube. The Donkey Speaks- Bitter and Sweet.