Sixth Century Greek theologian on Particular Redemption

Regarding the way in which he was slaughtered, the flowing blood was given as the price on behalf of those who are saved. And since he was crucified not on behalf of a portion or [on behalf] of one nation of men, he purchased by his blood [some] from every tribe of Israel and every language of men and indeed of [every] people.

Anonymous Greek Scholiast, in Fathers of the Church, Vol. 144, Cassiodorus, St. Gregory the Great, and Anonymous Greek Scholia, Writings on the Apocalypse, Scholia 29, p. 131 T.C. Schmidt, Trans.

Alternative translation:

Subsequent to the slaughter that was so executed, the blood that was shed was the price given for the redemption of those saved. Furthermore, since he was crucified for the sake of not just a part of humanity or of one nation only, he has redeemed by his blood people out of every tribe of Israel and of every human tongue, and, yes, of every people.

Cassian the Sabaite(?), An Ancient Commentary on the Book of Revelation: a Critical Edition of the Scholia in Apocalypsin, P. Tzamalikos trans. (p. 133)   

Sixth Century Greek theologian on the Key of David

"Holy, true," not through participation, but being such in essence. He himself is God the Word, having the key of David. For when the Word became flesh, he opens the Scriptures by this key [Scriptures], which were shut before [his] advent [and] which no one is able to shut by asserting that they have not been fulfilled.

Anonymous Greek Scholiast (possibly drawing from Didymus the Blind), in Fathers of the Church, Vol. 144, Cassiodorus, St. Gregory the Great, and Anonymous Greek Scholia, Writings on the Apocalypse, Scholia 20, p. 121 T.C. Schmidt, Trans.

Alternative translation:

He that is holy, he that is true: This is God the Logos, who is what He is not by participation, but by essence. Who hath the key of David: when the Logos became flesh, through this key he openeth the scriptures, which were sealed before the advent, that no man can shut since he declares them not [yet] fulfilled.

Cassian the Sabaite(?), An Ancient Commentary on the Book of Revelation: a Critical Edition of the Scholia in Apocalypsin, P. Tzamalikos trans. (p. 133)   

Gregory the Great: the Woman of Revelation 12 is the Church

In a similar manner, John said: A woman clothed with the sun and with the moon under her feet (Rv 12.1). For by the "sun" is understood the illumination of truth, whereas by the "moon," which wanes when the month is completed, the changeableness of temporal existence. But because the holy Church is protected by the splendor of light from above, she is, as it were, clothed with the sun. But because she despises all temporal things, she tramples the moon under her feet.

Gregory the Great, From Moralia 34.14 [25], 1-15. CCSL 143B: 1750. in Fathers of the Church, Vol. 144, Cassiodorus, St. Gregory the Great, and Anonymous Greek Scholia, Writings on the Apocalypse, Section 24, p. 65 Mark DelCogliano, Trans.

Cassiodorus on the Woman of Revelation 12

But he touches upon a few things concerning the Lord Jesus Christ and his mother, and concerning the opposition of the devil. Joining past things with future things, he says that God ascended to heaven and that his mother was to be preserved at a certain time in secret places, that he might nourish her there for three-and-a-half years. This passage, as Tyconius relates, contains great mystery.[FN42]

...

Again, there is a mention of Christ the Lord and his mother, in that the devil, believing that he could hurt the mother, sent from his mouth an immense river and thought that it would drown her. But she, having been taken to a very safe place, evaded the poison of diabolic fraud.

[FN 42. Cf. Eph 5.32; Tyconius (Exposition of the Apocalypse, on Rv 12.6, CCSL 107A: 178, FC 134: 127) wrote that the woman nourished for one thousand two hundred sixty days symbolizes the Church nourished on heavenly teaching from the birth of Christ up to the end of the world.] 

Cassiodorus (footnote is translator's) in Fathers of the Church, Vol. 144, Cassiodorus, St. Gregory the Great, and Anonymous Greek Scholia, Writings on the Apocalypse, Chapter 12, section 16. [1-6] and [13-16], pp. 27-28 Francis X. Gumerlock, Trans.

Cassiodorus: Angel can refer to Bishop

And to the angel of the church of Smyrna, write: The first and the last says these things, etc. He advises that the should write to the angel of Smyrna, that is, to the bishop; for that passage in the Acts of the Apostles testifies that a bishop is called an angel, where Peter comes and knocks on the door of the apostles, and it is said, "It is not Peter, but his angel."[FN22]

[FN22: Acts 9.15, Interestingly, Tyconius used this passage in Acts to prove that "angel" in Acts 9.15 meant Peter's own "spirit," and that John used the word "angel," not for the bishop of the church addressed in the letters in Rv 2 and 3, but as a metonymy for the Church itself. See Tyconius, Exposition of the Apocalypse, on Rv 1.19-20. CCSL 107A: 110, FC 134: 36.

Cassiodorus (footnote is translator's) in Fathers of the Church, Vol. 144, Cassiodorus, St. Gregory the Great, and Anonymous Greek Scholia, Writings on the Apocalypse, Chapter 2, section 5. [8], p. 19, Francis X. Gumerlock, Trans.

God's Will Decides Morality

What is done in accordance with God's will is the best of all things even if it seems to be bad. What is done contrary to God's will and decree is the worst and most unlawful of things--even if men judge that it is very good. Suppose someone slays another in accordance with God's will. This slaying is better than any loving-kindness. Let someone spare another and show him great love and kindness against God's decree. To spare the other's life would be more unholy than any slaying. For it is God's will and not the nature of things that makes the same actions good or bad. Fathers of the Church (vol. 68), St. John Chrysostom, Discourses Against Judaizing Christians, translated by Paul W. Harkins, Discourse IV, section I, paragraph 6 (p. 74)

Circumcision's Relation to Baptism - Paul W. Harkins regarding Chrysostom and Aphrahat

But someone might say: "Is there so much harm in circumcision that it makes Christ's whole plan of redemption[fn9] useless?" Yes, the harm of circumcision is as great as that, not because of its own nature but because of your obstinacy. FN9: Redemption is based on Christ's Incarnation; we participate in it by baptism, not circumcision. Cf. ACW 31.161-62, 232, 328. To accept circumcision is to embrace the Old Law in its entirety; but God has rejected the Old Covenant, and what God has rejected can no longer be good or useful because it is now contrary to his will. Aphrahat, the first great father of the Iranian Church and a contemporary of Chrysostom, also maintained that circumcision never had any salvific value except where combined with faith, and Israel was unfaithful, as the prophets themselves contended. See J. Neusner, "The Jewish-Christian Argument in Fourth-Century Iran: Aphrahat on Circumcision, the Sabbath, and the Dietary Laws," Journal of Ecumenical Studies 7 (1970) 282-90. The Fathers of the Church, vol. 68, St. John Chrysostom, Discourses Against Judaizing Christians, translated by Paul W. Harkins, Discourse II, section (6), p. 37.