Ambrosius Autpertus (an 8th century priest, who wrote commentaries on Holy Scripture and on the lives of the saints, and is venerated as a saint within the Roman Catholic Church) on Revelation 20:10.
But when it is said, "and they shall be tormented day and night for ages of ages (saecula saeculorum)," it is not to be taken in such a way that no sentence of God’s mercy remains: but because very long ages are appointed for punishments, which human frailty cannot measure. For it can happen that even the evil spirits themselves, who are now obstinate in their wickedness, after long ages (post longa saecula) are freed by God’s mercy, when they put off the nature which they corrupted, and are reformed to that for which they were created. But if this is so, it does not detract from divine justice, because for a long and great while they will pay what they deserved.
--Ambrosius Autpertus, Commentarius in Apocalypsin, Liber X, Caput 36
Patrologia Latina, Vol. 89, col. 1391A-1391C
Written c. 770-784 AD at San Vincenzo al Volturno.
Original Latin Text
Sed cum dicitur, et cruciabuntur die ac nocte in saecula saeculorum, non ita accipiendum est quasi nulla Dei misericordiae sententia remaneat: sed quia longa valde saecula poenis statuta sunt, quae humana fragilitas metiri non potest. Potest enim fieri ut etiam ipsi maligni spiritus, qui nunc in sua nequitia obstinati sunt, post longa saecula Dei misericordia liberentur, quando deposita natura quam corruperant, reformantur ad id in quo creati sunt. Quod si ita est, non detrahitur divinae justitiae, quia diu multumque quod meruerunt solvent.
Erasmus of Rotterdam (1466--1536.)
"For all of God’s discipline is medicinal, and is intended for correction rather than destruction."
--Erasmus, Handbook of the Christian Soldier, 1503.
[Source: Collected Works of Erasmus Vol. 66, trans. Charles Fantazzi, University of Toronto Press]
Isidore of Seville, Archbishop (d. 636)
"God does not punish in order to take vengeance, but in order to heal."
--Isidore of Seville, Sententiae Book 2, Chapter 7, circa 620 AD