On the Necessity of a Council, Even When Confronting Previously Condemned Heresies

For, it is not a question of danger concerning only one church; nor are there two or three churches which have fallen in this bitter storm. In fact, the evil of heresy is spread almost from the mountains of Illyricum to the Thebaid. Its pernicious seeds were formerly sown by the detestable Arius, and, having taken deep root because of the many who in the meantime diligently cultivated the impiety, they have now produced their destructive fruit. For, the doctrines of true religion have been overthrown and the laws of the Church have been made void….

Now, by what means you will give help in our troubles and how you will show sympathy to the afflicted, you will certainly not need to learn from us, but from the Holy Spirit Himself who will suggest it to you. Only, there is need of haste to save those who still remain, and of the presence of more brethren so that those coming here may make up the full number of a synod, to the end that they may have the prestige to set matters right not only because of the dignity of those sending them, but also from their own number; and that they may restore the creed written in Nicaea by our Fathers, banish the heresy by proclamation, and discuss with the churches matters pertaining to peace, bringing together into harmony those who are of the same belief… On this account, we especially need help from you, in order that those professing the faith of the Apostles, after putting an end to the schisms which they devised, may become subject for the future to the authority of the Church, so that the body of Christ being restored to soundness in all its members may be made perfect, and that we may not only rejoice over the blessings of others, as we now do, but may also behold our own churches regaining the ancient glory of Orthodoxy.

- St Basil the Great, Letter No. 92 to the Bishops of Italy and Gaul, written in 372 A.D., 47 years after the First Ecumenical Synod at Nicaea condemned Arianism.