Augustine of Hippo — as excerpted in the Catena Aurea on Mark 9:43-50

“(de Civ. Dei, 21.9) But those who hold that both of these, namely, the fire and the worm, belong to the pains of the soul, and not of the body, say also that those who are separated from the kingdom of God are tortured, as with fire, by the pangs of a soul, repenting too late, and hopelessly; and they not unfitly contend that fire may be put for that burning grief, as says the Apostle, Who is offended, and I burn not? (2 Cor. 11:29) They also think that by the worm must be understood the same grief, as is said: As a moth destroys a garment, and a worm wood, so grief tortures the heart of man. (Prov. 25:20. vulg.) All those who hesitate not to affirm that there will be pain both of body and soul in that punishment, affirm that the body is burnt by the fire. But although this is more credible, because it is absurd that there either the pains of body or of soul should be wanting, still I think that it is easier to say that both belong to the body than that neither; and therefore it seems to me that Holy Scripture in this place is silent about the pains of the soul, because it follows that the soul also is tortured in the pains of the body. Let each man therefore choose which he will, either to refer the fire to the body, the worm to the soul, the one properly, the other in a figure, or else both properly to the body; for living things may exist even in fire, in burnings without being wasted, in pain without death, by the wondrous power of the Almighty Creator. It goes on: And if thy foot offend thee, cut it off: it is better for thee to enter halt into life, than having two feel to be cast into hell, into the fire that never shall be quenched; where their worm, dieth not, and the fire is not quenched.”