Catena Aurea on Mark 9:43–50: Pseudo-Chrysostom

Then He introduces the witness of prophecy from the prophet Isaiah, saying, “Where their worm dieth not, and the fire is not quenched.” [Isa 65:24] He says not this of a visible worm, but He calls conscience, a worm, gnawing the soul for not having done any good thing; for each of us shall be made his own accuser, by calling to mind what he has done in this mortal life, and so their worm remains forever.