Now, because no description can deal adequately with the gravity of God’s vengeance against the wicked, their torments and tortures are figuratively expressed to us by physical things, that is, by darkness, weeping, and gnashing of teeth (Mt. 8:12; 22:13), unquenchable fire (Mt. 3:12; Mk. 9:43; Isa. 66:24), an undying worm gnawing at the heart (Isa. 66:24). By such expressions the Holy Spirit certainly intended to confound all our senses with dread.
John Calvin