St. Basil (Doctor of The Church. Bishop of Cappadocia from 370 A.D. until his death in 379 A.D.)
We have heard before how many names of the Lord we have already been taught by the prophet. ‘Behold, a virgin shall conceive in her womb and shall bear a Son, and they shall call his name Emmanuel.’ Here His name is called ‘Messenger of great counsel’. He is the one Who made known the great counsel kept secret for the ages (Col. 1:26) and not manifested to other generations (Eph. 3:5). He is the one Who announced and manifested among the Gentiles His inscrutable wealth (Eph. 5:8), in order that the Gentiles should be fellow-heirs and the same body (Eph. 3:6) of Him whose sovereignty is upon His shoulder, that is Whose kingdom and power are on the cross; as having been lifted up on the cross He drew all to Himself (John 12:32). […] There is no end of His peace, for the reason that it is a supramundane gift. For had it been from the world, it would have lasted only as long as the world exists. But now, he who has accepted His peace and preserved it shall live with the good things of His peace for ever. The peace of Solomon was limited to the recorded years, whereas the peace from the Lord is co-extensive with the whole of eternity, being unlimited and boundless. For all shall be subjected to Him and all shall recognise His mastery, and when God shall be all in all (1 Cor. 15:28), and those making an uproar by their apostasies are silenced, all in peaceful harmony shall praise God with hymns.
--St. Basil the Great, Commentary on the Prophet Isaiah, translated by Nikolai A. Lipatov, p. 275-276
Gregory Nazianzus (Doctor of The Church. Bishop of Constantinople from 379 to 390 A.D.)
"These, if they will, may go Christ's way, but if not let them go their way. In another place perhaps they shall be baptized with fire, that last baptism, which is not only painful, but enduring also; which eats up, as if it were hay, all defiled matter, and consumes all vanity and vice."
--Oracles 39:19
Gregory of Nyssa (Bishop of Nyssa from 372 to 376 and from 378 until his death in 394. Venerated as a Saint by Orthodox, Catholics, and Anglicans. Declared the Father of Fathers by the Seventh Ecumenical Council)
For it is as when some worthless material has been mixed with gold, and the gold-refiners burn up the foreign and refuse part in the consuming fire, and so restore the more precious substance to its natural lustre: not that the separation is effected without difficulty, for it takes time for the fire by its melting force to cause the baser matter to disappear; but for all that, this melting away of the actual thing that was embedded in it to the injury of its beauty is a kind of healing of the gold. In the same way when death, and corruption, and darkness, and every other offshoot of evil had grown into the nature of the author of evil, the approach of the Divine power, acting like fire, and making that unnatural accretion to disappear, thus by purgation of the evil becomes a blessing to that nature, though the separation is agonizing. Therefore even the adversary himself will not be likely to dispute that what took place was both just and salutary, that is, if he shall have attained to a perception of the boon. For it is now as with those who for their cure are subjected to the knife and the cautery; they are angry with the doctors, and wince with the pain of the incision; but if recovery of health be the result of this treatment, and the pain of the cautery passes away, they will feel grateful to those who have wrought this cure upon them.
St. Gregory of Nyssa, The Catechetical Oration, Chapter 38. Translated by William Moore and Henry Austin Wilson. In Nicene and Post-Nicene Fathers, Second Series, Volume 5. Edited by Philip Schaff and Henry Wace. Buffalo: Christian Literature Publishing Co., 1893.
“For it is clear that God will be ‘all in all’ when there shall be no evil remaining in existence.”
--On the Soul and the Resurrection
St. Ambrose (Doctor of The Church. Bishop of Milan from 374 A.D. to 397 A.D. Venerated as Saint by Catholics and Orthodox)
The Savior has set forth in the Apocalypse two kinds of resurrection: “Blessed is he who has a part in the first resurrection,” [Rev 20:6] for those who come to grace do so without judgment. But as for those who do not come to the first, but are reserved for the second resurrection, these will be chastised until the appointed times are fulfilled — that is, between the first and the second resurrection. And if they have not yet made satisfaction, they will remain longer in punishment, until they pay the last farthing.
--St. Ambrose, PL 14, col. 924 - Enarratio in Psalmum I, §36.
And
"When therefore, all things have become subject to Christ, through Christ's obedience, so that all bend their knees in His name, then He Himself will be all in all. For now, since all do not believe, all do not seem to be in subjection. But when all have believed and done the will of God, then Christ will be all and in all."
--Exposition of the Christian Faith (also known as De Fide ad Gratianum), Book V, Chapter 14, Section 181
Also
"The mystery of the cross of the Lord is a heavenly thing; and it was wrought not only for men, but also for the angels. For those who are in the heavens may be confirmed, and those who are in the lower parts may be restored."
--De fide ad Gratianum (on the Christian Faith), Book I, Chapter 5 section 43.