Chapter 23.–Against Those Who are of Opinion that the Punishment Neither of the Devil Nor of Wicked Men Shall Be Eternal.
First of all, it behoves us to inquire and to recognize why the Church
has not been able to tolerate the idea that promises cleansing or
indulgence to the devil even after the most severe and protracted
punishment. For so many holy men, imbued with the spirit of the Old
and New Testament, did not grudge to angels of any rank or character
that they should enjoy the blessedness of the heavenly kingdom after
being cleansed by suffering, but rather they perceived that they could
not invalidate nor evacuate the divine sentence which the Lord
predicted that He would pronounce in the judgment, saying, “Depart from
me, ye cursed, into everlasting fire, prepared for the devil and his
angels.”  For here it is evident that the devil and his angels
shall burn in everlasting fire. And there is also that declaration in
the Apocalypse, “The devil their deceiver was cast into the lake of
fire and brimstone, where also are the beast and the false prophet.
And they shall be tormented day and night for ever.”  In the
former passage “everlasting” is used, in the latter “for ever;” and by
these words Scripture is wont to mean nothing else than endless
duration. And therefore no other reason, no reason more obvious and
just, can be found for holding it as the fixed and immovable belief of
the truest piety, that the devil and his angels shall never return to
the justice and life of the saints, than that Scripture, which deceives
no man, says that God spared them not, and that they were condemned
beforehand by Him, and cast into prisons of darkness in hell, 
being reserved to the judgment of the last day, when eternal fire shall
receive them, in which they shall be tormented world without end. And
if this be so, how can it be believed that all men, or even some, shall
be withdrawn from the endurance of punishment after some time has been
spent in it? how can this be believed without enervating our faith in
the eternal punishment of the devils? For if all or some of those to
whom it shall be said, “Depart from me, ye cursed, into everlasting
fire, prepared for the devil and his angels,”  are not to be
always in that fire, then what reason is there for believing that the
devil and his angels shall always be there? Or is perhaps the sentence
of God, which is to be pronounced on wicked men and angels alike, to be
true in the case of the angels, false in that of men? Plainly it will
be so if the conjectures of men are to weigh more than the word of
God. But because this is absurd, they who desire to be rid of eternal
punishment ought to abstain from arguing against God, and rather, while
yet there is opportunity, obey the divine commands. Then what a fond
fancy is it to suppose that eternal punishment means long continued
punishment, while eternal life means life without end, since Christ in
the very same passage spoke of both in similar terms in one and the
same sentence, “These shall go away into eternal punishment, but the
righteous into life eternal!”  If both destinies are “eternal,”
then we must either understand both as long-continued but at last
terminating, or both as endless. For they are correlative,–on the one
hand, punishment eternal, on the other hand, life eternal. And to say
in one and the same sense, life eternal shall be endless, punishment
eternal shall come to an end, is the height of absurdity. Wherefore,
as the eternal life of the saints shall be endless, so too the eternal
punishment of those who are doomed to it shall have no end.
 Matt. xxv. 41.
 Rev. xx. 10.
 2 Pet. ii. 4.
 Matt. xxv. 41.
 Matt. xxv. 46.