As for John the glory of the Episcopate of Constantinople, whose holy life obtained p. 620 the reward of martyrdom without any show of Gentile persecution, hear what he thought and taught on the Incarnation of the Son of God: “And Him,” he says, “whom if He had come in unveiled Deity neither the heaven nor the earth nor the sea nor any other creature could have contained, the pure womb of a Virgin bore.” 2680 This mans faith and doctrine then, even if you ignore that of others, you ought to follow and hold, as out of love and affection for him the pious people chose you as their Bishop. For when it took you for its priest from the Church of Antioch, from which it had formerly chosen him, it believed that it would receive in you all that it had lost in him. 2681 Did not, I ask you, all these almost with prophetic spirit say all these things in order to confound your blasphemies. For you declare that our Lord and Saviour Christ is not God: they declare that Christ the Lord is Very God. You blasphemously assert that Mary is Christotocos not Theotocos: they do not deny that she is Christotocos, while they acknowledge her as Theotocos. Not merely the substance but the words also are opposed to your blasphemies: that we may clearly see that an impregnable bulwark was formerly prepared by God against your blasphemies, to break on the wall of truth ready prepared, the force of the heretical attack which was at some time or other to come. And you, O you most wicked and shameless contaminator of an illustrious city, you disastrous and deadly plague of a Catholic and holy people, do you dare to stand and teach in the Church of God, and with your wild and blasphemous words slander the priests of an ever unbroken faith and Catholic confession, and say that the people of the city of Constantinople are in error through the fault of their earlier teachers? Are you then the corrector of former Bishops, the accuser of ancient priests, are you better than Gregory, more approved than Nectarius, greater than John, 2682 and all the other Bishops of Eastern cities who, though not of the same renown as those whom I have enumerated, were yet of the same faith? which, as far as the matter in hand is concerned, is enough: for when it is a question of the faith, all are as good as the best in so far as they agree with the best.
S. Chrysostom had been taken from Antioch for the Bishopric of Constantinople: and after the death of Sisinnius in 426, as there was so much rivalry and party spirit displayed at Constantinople, the Emperor determined that none of that Church should fill the vacant see, but sent for Nestorius from Antioch, where he had already gained a great reputation for eloquence (cf. Socrates H. E. VII. xxix.). It is to the fact that both S. Chrysostom and Nestorius came from the same city that Cassian alludes in the text.620:2682
The reference is to Gregory Nazianzen, Bishop of Constantinople from 379 to 381 when he retired in the interests of peace; to Nectarius who was chosen to succeed him, and occupied the post from 381 to 397; and to his successor, S. John Chrysostom 397 to 404.