From City of God, 20.25 (426)
The prophet Malachi… predicts the last judgment, saying, “Behold, he comes, says the Lord Almighty; and who shall abide the day of his entrance? . . . for I am the Lord your God, and I change not,” (Mal. 3:1-6).
From these words it more evidently appears that some shall in the last judgment suffer some kind of purging punishments; for what else can be understood by the word, “Who shall abide the day of his entrance, or who shall be able to look upon him? For he enters as a molder’s fire, and as the herb of fullers: and he shall sit fusing and purifying as if over gold and silver: and he shall purify the sons of Levi, and pour them out like gold and silver?” Similarly, Isaiah says, “The Lord shall wash the filthiness of the sons and daughters of Zion, and shall cleanse away the blood from their midst, by the spirit of judgment and by the spirit of burning” (Isa. 4:4).
Unless perhaps we should say that they are cleansed from filthiness and in a manner clarified, when the wicked are separated from them by penal judgment, so that the elimination and damnation of the one party is the purgation of the others, because they shall henceforth live free from the contamination of such men.
But when he says, “And he shall purify the sons of Levi, and pour them out like gold and silver, and they shall offer to the Lord sacrifices in righteousness; and the sacrifices of Judah and Jerusalem shall be pleasing to the Lord,” he declares that those who shall be purified shall then please the Lord with sacrifices of righteousness, and consequently they themselves shall be purified from their own unrighteousness which made them displeasing to God.
Now they themselves, when they have been purified, shall be sacrifices of complete and perfect righteousness; for what more acceptable offering can such persons make to God than themselves? But this question of purgatorial punishments we must defer to another time, to give it a more adequate treatment.
By “the sons of Levi” and “Judah and Jerusalem” we ought to understand the Church herself, gathered not from the Hebrews only, but from other nations as well; nor such a Church as she now is, when “if we say that we have no sin, we deceive ourselves, and the truth is not in us” (1 John 1:8), but as she shall then be, purged by the last judgment as a threshing-floor by a winnowing wind, and those of her members who need it being cleansed by fire, so that there remains absolutely not one who offers sacrifice for his sins. For all who make such offerings are assuredly in their sins, for the remission of which they make offerings, that having made to God an acceptable offering, they may then be absolved.
St. Augustine (354-430) was a theologian and philosopher who served as Bishop of Hippo Regius in North Africa. He was a voluminous author, whose writings about God’s grace, the Sacraments, and the Church have been profoundly influential in the development of Western Christianity. City of God, widely considered his greatest work, seeks to exonerate Christianity from blame for the Fall of Rome and probes major questions about sin and grace, the problem of evil and divine providence. His feast day is August 26.