But he could not hold the episcopate, even if he had before been made bishop, since he has cut himself off from the body of his fellow bishops, and from the unity of the Church; since the apostle admonishes that we should mutually sustain one another, and not withdraw from the unity which God has appointed, and says,
Bearing with one another in love, endeavouring to keep the unity of the Spirit in the bond of peace. Eph. 4:2-3 He then who neither maintains the unity of the Spirit nor the bond of peace, and separates himself from the band of the Church, and from the assembly of priests, can neither have the power nor the honour of a bishop, since he has refused to maintain either the unity or the peace of the episcopate. (Letter 51)
St. Basil of Caesarea ca. 330-379
The first separatists had received their ordination from the Fathers, and possessed the spiritual gift by the laying on of their hands. But they who were broken off had become laymen, and, because they are no longer able to confer on others that grace of the Holy Spirit from which they themselves are fallen away, they had no authority either to baptize or to ordain. And therefore those who were from time to time baptized by them, were ordered, as though baptized by laymen, to come to the church to be purified by the Church’s true baptism. (Letter 188: Canon 1)
St. Maximus the Confessor 580-662
“And you still refuse to enter into communion with the Patriarchate of Constantinople?” they asked.
“Still,” he answered.
They asked, “Why so?”
“Because the leaders of this Church have rejected the definitions of four holy councils and accepted the Nine Chapters published in Alexandria; the Ekthesis written by Sergius, Patriarch of Constantinople; and the recently issued Typos. What they proclaimed as dogma in the Ekthesis they rejected in the Typos. They have repeatedly excommunicated themselves from the Church and are completely unstable in the faith. Additionally, they have been cut off and stripped of priesthood by the local council held at Rome. What Mysteries, then, can they perform? And what spirit descends on those whom they ordain?” (St. Dimitri Rostov: Life of St. Maximus)