Holy Scripture plainly declares that at least some souls will be saved through fire. 1 Cor 3:13 Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by 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 shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire." There are only two real ways of understanding this verse, Apokatastasis and Purgatory. Either everyone is saved through fire, or at least some souls will be, if anyone is not a universalist therefore, he should believe in purgatory. St. Gregory of Nyssa, St. Clement of Alexandria, St. Isaac of Syria and many others clearly describe a fire of purification before the end of time, St. Gregory writes, "But as for those whose weaknesses have become inveterate, and to whom no purgation of their defilement has been applied, no mystic water, no invocation of the Divine power, no amendment by repentance, it is absolutely necessary that they should come to be in something proper to their case,—just as the furnace is the proper thing for gold alloyed with dross,—in order that, the vice which has been mixed up in them being melted away after long succeeding ages, their nature may be restored pure again to God" http://www.ccel.org/ccel/schaff/npnf205.xi.ii.xxxvii.html
Elsewhere, he wrote "When he has quitted his body and the difference between virtue and vice is known he cannot approach God till the purging fire shall have cleansed the stains with which his soul was infested. That same fire in others will cancel the corruption of matter, and the propensity to evil." Its clear the Fathers use the imagery of fire to express the nature of purification, which will be more or less painful the more a man is attached to sin, or has neglected penance and sanctification in this life. In the Bible, we read of Dives in Hades, "Lk 16:24‘Father Abraham, have pity on me and send Lazarus to dip the tip of his finger in water and cool my tongue, because I am in agony in this fire." In Tobit 13:2, "For he doth scourge, and hath mercy: he leadeth down to hades, and bringeth up again" Since St. Isaac etc held that all of Hades is intrinsically purgatorial, why should anyone object to fire - the description handed down both by Scripture and Tradition - being used to denote the painful purifications of the intermediate state before judgment day?
Another Saint Gregory, Pope Gregory I of Rome, like St. Augustine, takes the near-universal belief in some sort of purgatorial purification for granted, rather, St. Gregory the Great is keen to lay down as a principle that there are some sins that incur eternal penalty, "the Apostle said not that he may be saved by fire, that buildeth upon this foundation iron, brass, or lead, that is, the greater sort of sins, and therefore more hard, and consequently not remissible in that place: but wood, hay, stubble, that is, little and very light sins, which the fire doth easily consume." (Dialogues, Book 4, Chapter 39) http://www.tertullian.org/fathers/gregory_04_dialogues_book4.htm
The Lord's statement "He who utters blasphemy against the Holy Spirit has no forgiveness, either in this world or the world to come" is understood by Pope Gregory thus, "Out of which sentence we learn, that some sins are forgiven in this world, and some other may be pardoned in the next: for that which is denied concerning one sin, is consequently understood to be granted touching some other". Likewise, the Lord speaks of those who will not get out from prison until they have paid the last penny (Mat 5:26), St. Peter also mentions this prison of spirits where Christ went and preached (1 Pet 3:19-20) and so it is clear the Bible mentions temporary punishment that will have an end (but which will be painful if we've lived in sin) alongside eternal. So, why the objection to purgatory, granted that all Apostolic Churches agree "it is a pious and holy thought to pray for the dead, that they may be loosed from their sins"(2 Macc 12:46)?