Observe, now, here at the very beginning, how, in ridiculing the doctrine of a conflagration of the world, held by certain of the Greeks who have treated the subject in a philosophic spirit not to be depreciated, he would make us, “representing God, as it were, as a cook, hold the belief in a general conflagration;” not perceiving that, as certain Greeks were of opinion (perhaps having received their information from the ancient nation of the Hebrews), it is a purificatory fire which is brought upon the world, and probably also on each one of those who stand in need of chastisement by the fire and healing at the same time, seeing it burns indeed, but does not consume, those who are without a material body, which needs to be consumed by that fire, and which burns and consumes those who by their actions, words, and thoughts have built up wood, or hay, or stubble, in that which is figuratively termed a “building.” And the holy Scriptures say that the Lord will, like a refiner's fire and fullers' soap, visit each one of those who require purification, because of the intermingling in them of a flood of wicked matter proceeding from their evil nature; who need fire, I mean, to refine, as it were, (the dross of) those who are intermingled with copper, and tin, and lead. And he who likes may learn this from the prophet Ezekiel. But that we say that God brings fire upon the world, not like a cook, but like a God, who is the benefactor of them who stand in need of the discipline of fire, will be testified by the prophet Isaiah, in whose writings it is related that a sinful nation was thus addressed: “Because you have coals of fire, sit upon them: they shall be to you a help.” Now the Scripture is appropriately adapted to the multitudes of those who are to peruse it, because it speaks obscurely of things that are sad and gloomy, in order to terrify those who cannot by any other means be saved from the flood of their sins, although even then the attentive reader will clearly discover the end that is to be accomplished by these sad and painful punishments upon those who endure them. It is sufficient, however, for the present to quote the words of Isaiah: “For My name's sake will I show Mine anger, and My glory I will bring upon you, that I may not destroy you.” We have thus been under the necessity of referring in obscure terms to questions not fitted to the capacity of simple believers, who require a simpler instruction in words, that we might not appear to leave unrefuted the accusation of Celsus, that “God introduces the fire (which is to destroy the world), as if He were a cook.”
Source: Against Celsus (New Advent)