From an Orthodox Christian perspective, I can say that our Church knows nothing about the popular concept of a Rapture for 2,000 years and counting, and is well-acquainted with grief and tribulation, so after some confusion is dissipated I can see how this book fits in and look into it as a warning.
Looks like he is referring to the pretributarian rapture, not the rapture per se.
I think the author may be confused as well. the Rapture philosophy been a point of contention since it’s invention in the 1800s