Taken in its most plain sense, 1 Cor 3:13-15 plainly declares that there is a Purgatorial fire, in which certain lesser sins are purged.
"[13] Every man's work shall be manifest; for the day of the Lord shall declare it, because it shall be revealed in fire; and the fire shall try every man's work, of what sort it is. [14] If any man's work abide, which he hath built thereupon, he shall receive a reward. [15] If any man's work burn, he shall suffer loss; but he himself shall be saved, yet so as by fire." This is that prison of which the Lord speaks into which the adversary, the devil, will try to cast us, and from which no man goes forth until he has paid the last farthing; thus St. Caesarius, St. Cyprian and several other Fathers. Then, the Lord Himself says one particular sin is forgiven neither in this world, nor even in the world to come; from which the holy Fathers, such as St. Augustine, St. Isidore and Pope St. Gregory the Great, deduce or infer that other lesser sins, that is not the mortal sin of blasphemy against the Holy Ghost, are forgiven in the world to come, i.e. in Purgatory. These same Fathers apply those words of 1 Cor 3:13-15 to the lesser sins, or venial sins, needing to be burned up in the fire.
The CE explains: "There are several passages in the New Testament that point to a process of purification after death. Thus, Jesus Christ declares (Matthew 12:32): "And whosoever shall speak a word against the Son of man, it shall be forgiven him: but he that shall speak against the Holy Ghost, it shall not be forgiven him, neither in this world, nor in the world to come." According to St. Isidore of Seville (Deord. creatur., c. xiv, n. 6) these words prove that in the next life "some sins will be forgiven and purged away by a certain purifying fire." St. Augustine also argues "that some sinners are not forgiven either in this world or in the next would not be truly said unless there were other [sinners] who, though not forgiven in this world, are forgiven in the world to come" (City of God XXI.24). The same interpretation is given by Gregory the Great (Dial., IV, xxxix); St. Bede (commentary on this text); St. Bernard (Sermo lxvi in Cantic., n. 11) and other eminent theological writers.
A further argument is supplied by St. Paul in 1 Corinthians 3:11-15: ... it is regarded by many of the Fathers and theologians as evidence for the existence of an intermediate state in which the dross of lighter transgressions will be burnt away, and the soul thus purified will be saved. This, according to Bellarmine (De Purg., I, 5), is the interpretation commonly given by the Fathers and theologians; and he cites to this effect:
St. Ambrose (commentary on the text, and Sermo xx in Ps. cxvii),
St. Jerome, (Comm. in Amos, c. iv),
St. Augustine (Enarration on Psalm 37),
St. Gregory (Dial., IV, xxxix), and
Origen (Hom. vi in Exod.)."
http://www.newadvent.org/cathen/12575a.htmGiven all this, why do some Protestants, and some Orthodox, still deny the Apostolic, Biblical, Catholic and Patristic Doctrine of Purgatory? Some other Fathers:
https://www.catholicbridge.com/catholic/purgatory-church-fathers.phpOrigen: "If a man departs this life with lighter faults, he is condemned to fire which burns away the lighter materials, and prepares the soul for the kingdom of God, where nothing defiled may enter ... It is manifest that the fire destroys the wood of our transgressions and then returns to us the reward of our great works. (Patres Groeci. XIII, col. 445, 448 [A.D. 185-232]).
Tertullian: That allegory of the Lord [Matt. 5:25-26] . . . is extremely clear and simple in its meaning . . . [beware lest as] a transgressor of your agreement, before God the judge . . . and lest this judge deliver you over to the angel who is to execute the sentence, and he commit you to the prison of hell, out of which there will be no dismissal until the smallest even of your delinquencies be paid off in the period before the resurrection. What can be a more fitting sense than this? What a truer interpretation? (The Soul 35 [A.D. 210]).
Cyprian: It is one thing to stand for pardon, another thing to attain to glory; it is one thing, when cast into prison, not to go out thence until one has paid the uttermost farthing; another thing at once to receive the wages of faith and courage. It is one thing, tortured by long suffering for sins, to be cleansed and long purged by fire; another to have purged all sins by suffering. It is one thing, in fine, to be in suspense till the sentence of God at the Day of judgment; another to be at once crowned by the Lord (Letters 51[55]:20 [A.D. 253]).
Cyril of Jerusalem: Then we make mention also of those who have already fallen asleep: first, the patriarchs, prophets, apostles, and martyrs, that through their prayers and supplications God would receive our petition, next, we make mention also of the holy fathers and bishops who have already fallen asleep, and, to put it simply, of all among us who have already fallen asleep. For We believe that it will be of very great benefit to the souls of those for whom the petition is carried up, while this holy and most solemn sacrifice is laid out (Catechetical Lectures 23:5:9 [A.D. 350]).
John Chrysostom: Not in vain was it decreed by the apostles that in the awesome mysteries remembrance should be made of the departed. They knew that here there was much gain for them, much benefit. When the entire people stands with hands uplifted, a priestly assembly, and that awesome sacrificial victim is laid out, how, when we are calling upon God, should we not succeed in their defense? But this is done for those who have departed in the faith, while even the catechumens are not reckoned .is worthy of this consolation, but are deprived of every means of assistance except one. And what is that? We may give alms to the poor on their behalf (Homilies on Philippians 3:9-10 [A.D. 402]).
St. Clement: "In the other life there will be two fires, a 'devouring and consuming' one for the incorrigible, and for the rest, a fire that 'sanctifies' and 'does not consume, like the fire of the forge,' a 'prudent, intelligent' fire which penetrates the soul that passes through it." (Clement of Alexandria, Stromata 8.6, c. before 215 A.D.)
St. Basil the Great: "...and if they [i.e., Christians who die] are found to have any wounds from their wrestling, any stains or effects of sin, they are detained. If, however, they are found unwounded and without stain, they are, as unconquered, brought by Christ into their rest." (Basil, Homilies and Psalms, 370 A.D.)
And St. Basil's own brother,
St. Gregory of Nyssa declares: "...he [the departed soul] is not able to partake of divinity until he has been purged of the filthy contagion in his soul by purifying fire." (Sermon on the Dead)