A.T. Robertson Commentary Mark 9:48

"where their worm dieth not, and the fire is not quenched." — Mark 9:48 (ASV)

Their worm (ο σκωληξ αυτων). "The worm, i.e. that preys upon the inhabitants of this dread realm" (Gould). Two bold figures of Gehenna combined (the gnawing worm, the burning flame). No figures of Gehenna can equal the dread reality which is here described. See Isa 66:24.