Idolater
"Matthew 16:18-19" Dispensationalist (Catholic) χρ
This is from the late Bob Hill. His website was taken down by his son, from what I read here, after his passing. There is another one that specifically goes into the grammar. Which he in part repeats here. Aposticia is used in the NT a few times. They departed (apostasy) one place and went to another.
I think it's just talking about the Reformation. This is when all the millennial interpretation energy began in earnest, never really before the Reformation did anybody get too excited about whatever it meant, and then since the Reformation there's been a lot more interest in the topic. So I just think Paul's prophesying the Protestant Reformation, when all of a sudden in history, a thing never seen before, there were going to be a lot of Christians who weren't objectively committed to the Church anymore, but they're still Christians.