That point is explicitly addressed in the essay. There will be those who believe in Jesus and are killed after the Rapture of the Church. These are the ones who are gathered.
“There will be those who believe in Jesus and are killed after the Rapture of the Church. These are the ones who are gathered.”
Where does the Bible specify that?
Also, the verses in Matthew 24 are part of a discussion Jesus had with his disciples, who already believed, who were asking him how the end of the world would come about and Jesus was telling them what to watch for. If they would already be raptured by the time those things were taking place, then why would Jesus be bothering to tell them to watch out for those things that they would never see?
The pre-trib stuff is based partly on confusing tribulation with wrath. They are not the same thing. Jesus said we would have tribulation. There isn’t a single verse which divides the coming of Jesus for his church to rapture them and his return to judge the earth into two events. That passage in Matthew teaches that his coming to rapture his saints is a public event which the whole world will see and the rapture is part of his public return and happens right at the end. It is just a straightforward reading of the passage.