St. Ambrose of Milan ca. 338-397
That gnashing is not of bodily teeth, nor is that perpetual fire made up of physical flames, nor is the worm a bodily one. These things are spoken of, however, because, just as worms are born from massive overeating and fevers, so too, if anyone does not boil away his sins… he will be burned up in his own fire and devoured by his own worms. Whence also Isaias says: “Walk in the light of your fire, and the flame which you have ignited.” (Isa. 50:11) It is a fire which the gloominess of sins generates. It is a worm insofar as irrational sins of the soul stab at mind and heart and eat the guts out of your conscience. (Commentary on the Gospel of Luke, 7.205)