The ending is simply a simulation successful Sister Paxton's head:
"Sister Paxton is dying connected the floor, praying, sister Barnes has been dormant since Mr. Reed chopped her throat, and the last country is conscionable a simulation of sister Paxon's head. Like what the 3 of them discussed astir the prophet's revelation, the encephalon conscionable sees what it wants to spot earlier dying.
In the lawsuit of sister Paxton, she imagines immoderate benignant of divine justice: her person is miraculously inactive alive, conscionable successful clip to termination the monster (Reed). Paxton manages to halt the interior bleeding of her chopped and manages to get retired of the basement, find a mode retired of the house, and yet sees a butterfly posing connected her hand. As successful a mode to spot the light, then, astatine the past second, disappears, breaking the illusion."