Rapid Promotion of John to the Bishopric, and more Vehement Grappling with its Affairs. He re-establishes Discipline in the Churches everywhere. By sending an Embassy to Rome, he abolished the Hostility to Flavian
As soon as John was raised to the episcopal dignity, he devoted his attention first to the reformation of the lives of his clergy; he reproved and amended their ways and diet and every procedure of their manifold transactions. He also ejected some of the clergy from the Church. He was naturally disposed to reprehend the misconduct of others, and to antagonize righteously those who acted unjustly; and he gave way to these characteristics still more in the episcopate; for his nature, having attained power, led his tongue to reproof, and nerved his wrath more readily against the enemy.
He did not confine his efforts to the reformation of his own church; but as a good and large-minded man, he sought to rectify abuses throughout the world. Immediately upon entering the episcopate, he strove to put an end to the dissension which had arisen concerning Paulinus, between the Western and Egyptian bishops and the bishops of the East; since on this account a general disunion was overpowering the churches in the whole empire. He requested the assistance of Theophilus in effecting the reconciliation of Flavian with the bishop of Rome. Theophilus agreed to co-operate with him in the restoration of concord; and Acacius, bishop of Berea, and Isidore, whom Theophilus had proposed as a candidate for ordination instead of John, were sent on an embassy to Rome.
They soon effected the object of their journey, and sailed back to Egypt. Acacius repaired to Syria, bearing conciliatory letters to the adherents of Flavian from the priests of Egypt and of the West. And the churches, after a long delay once more laid aside their discord, and took up communion with one another. The people at Antioch, who were called Eustathians, continued, indeed, for some time to hold separate assemblies, although they possessed no bishop. Evagrius, the successor of Paulinus, did not, as we have stated, long survive him; and I think reconciliation became easier for the bishops from there being no one to oppose.
The laity, as is customary with the populace, gradually went over to those who assembled together under the guidance of Flavian; and thus, in course of time, they were more and more united.
Source: Ecclesiastical History (New Advent)