Did you think that verse refers to the present day church? It doesn’t. That passage is talking about the people who were not part of the church prior to the rapture but realized to late that we were right about Jesus being the only way to salvation. They are the ones who refused to take the mark of the beast and were slain for it.
Do a search on Tribulation Saints and do a little study. Here’s a place to start. http://tribulationsaints.com/definetribulationsaint.html
Regards,