Review from the comment
There's two movies inside of Apostle. The first is a thriller where a man suffering from PTSD after travels abroad is looking for his sister who is being held for ransom by a mysterious cult. This movie is pretty good. Its gorgeously shot, well paced, introduces lots of fleshed out characters and wraps up viewers into its snowballing tension. It also has a small undercurrent of something supernatural afoot.
Its that supernatural stuff that takes over in the third act, shifting from subtle to outright ridiculousness once the curtain is drawn back on everything that is going on. Its a dang shame too, because Apostle really had the punch to be something great.