Augustine wrote about the large variety of views of salvation that existed in his day, including some that involved some form of eternal security:
"I must now, I see, enter the lists of amicable controversy with those tender-hearted Christians who decline to believe that any, . . . of those whom the . . . Judge may pronounce worthy . . . hell, shall suffer eternally, and who suppose that they shall be delivered after a fixed term of punishment . . . In respect of this matter, Origen . . . believed that even the devil himself and his angels . . . should be delivered from their torment, . . . . But the Church, not without reason, condemned him for this and other errors...
There are others, . . . who, . . . attribute to God a still greater compassion towards men. . . . when the judgment comes, mercy will prevail. . . .
So, too, there are others who promise this deliverance from eternal punishment, not, indeed, to all men, but only to those who have been washed in Christian baptism, and who become partakers of the body of Christ, no matter how they have lived, or what heresy or impiety they have fallen into. They ground this opinion on the saying of Jesus, '. . . If a man eat of this bread, he shall live for ever.' Therefore, say they, it follows that these persons must be delivered from death eternal, and at one time or other be introduced to everlasting life.
There are others still who make this promise . . . only to the Catholics, however badly they have lived. . . . in the catholic Church, they shall not die eternally, but at one time or other obtain eternal life; and all that wickedness of theirs shall not avail to make their punishment eternal, but only proportionately long and severe....
But, say they [others], the catholic Christians have Christ for a foundation, and they have not fallen away from union with Him, no matter how depraved a life they have built on this foundation, as wood, hay, stubble; and accordingly the well-directed faith by which Christ is their foundation will suffice to deliver them some time from the continuance of that fire, though it be with loss, since those things they have built on it shall be burned." (The City Of God, 21:17-20, 21:22, 21:26)
Some other examples:
"Saint Jerome, though an enemy of Origen, was, when it came to salvation, more of an Origenist than Ambrose. He believed that all sinners, all mortal beings, with the exception of Satan, atheists, and the ungodly, would be saved: 'Just as we believe that the torments of the Devil, of all the deniers of God, of the ungodly who have said in their hearts, 'there is no God,' will be eternal, so too do we believe that the judgment of Christian sinners, whose works will be tried and purged in fire will be moderate and mixed with clemency.' Furthermore, 'He who with all his spirit has placed his faith in Christ, even if he die in sin, shall by his faith live forever.'" (Jacques Le Goff, The Birth Of Purgatory [Chicago, Illinois: The University of Chicago Press, 1986], p. 61)
"Jerome develops the same distinction, stating that, while the Devil and the impious who have denied God will be tortured without remission, those who have trusted in Christ, even if they have sinned and fallen away, will eventually be saved. Much the same teaching appears in Ambrose, developed in greater detail." (J.N.D. Kelly, Early Christian Doctrines [San Francisco, California: HarperCollins Publishers, 1978], p. 484)
"Like Hilary and Ambrose, Ambrosiaster distinguishes three categories: the saints and the righteous, who will go directly to heaven at the time of the resurrection; the ungodly, apostates, infidels, and atheists, who will go directly into the fiery torments of Hell; and the ordinary Christians, who, though sinners, will first pay their debt and for a time be purified by fire but then go to Paradise because they had the faith.
Commenting on Paul, Ambrosiaster writes: 'He [Paul] said: 'yet so as by fire,' because this salvation exists not without pain; for he did not say, 'he shall be saved by fire,' but when he says, 'yet so as by fire,' he wants to show that this salvation is to come, but that he must suffer the pains of fire; so that, purged by fire, he may be saved and not, like the infidels [perfidi], tormented forever by eternal fire; if for a portion of his works he has some value, it is because he believed in Christ.'" (Jacques Le Goff, The Birth Of Purgatory [Chicago, Illinois: The University of Chicago Press, 1986], p. 61)
"we find Ambrosiaster teaching that, while the really wicked, 'will be tormented with everlasting punishment', the chastisement of Christian sinners will be of a temporary duration." (J.N.D. Kelly, Early Christian Doctrines [San Francisco, California: HarperCollins Publishers, 1978], p. 484)