Just as those who refine gold from the dross which it contains not only get this base alloy to melt in the fire, but are obliged to melt the pure gold along with the alloy, and then while this last is being consumed the gold remains, so, while evil is being consumed in the purgatorial fire, the soul that is welded to this evil must inevitably be in the fire too, until the spurious material alloy is consumed and annihilated by this fire. If a clay of the more tenacious kind is deeply plastered round a rope, and then the end of the rope is put through a narrow hole, and then some one on the further side violently pulls it by that end, the result must be that, while the rope itself obeys the force exerted, the clay that has been plastered upon it is scraped off it with this violent pulling and is left outside the hole, and, moreover, is the cause why the rope does not run easily through the passage, but has to undergo a violent tension at the hands of the puller. In such a manner, I think, we may figure to ourselves the agonized struggle of that soul which has wrapped itself up in earthy material passions, when God is drawing it, His own one, to Himself, and the foreign matter, which has somehow grown into its substance, has to be scraped from it by main force, and so occasions it that keen intolerable anguish.
Then it seems, I said, that it is not punishment chiefly and principally that the Deity, as Judge, afflicts sinners with; but He operates, as your argument has shown, only to get the good separated from the evil and to attract it into the communion of blessedness.