Synesius of Cyrene (c.370-c.413) was a Neo-Platonic philosopher who became bishop of Ptolemais in the Cyrenaica. He left behind a small corpus of texts that offer much information about daily life in Late Antiquity, and about the christianization of the Roman world.
In his letter, Synesius warns the other clerics for a man named Quintianus, a follower of Eunomius of Cyzicus (†394). This Eunomius had formalized the doctrine of Arianism during the reign of Constantius II (337-361). Theodosius had outlawed Arianism, and during the reign of his son Arcadius - in the age of Synesius - his books had been burnt (some fragments remain, though).
The text of Letter 5, written in 412, is offered here in the translation by A. Fitzgerald.
Letter 5: The Arian Controversy
 To the Bishops
It is well to trust in God, rather than to trust in man.note[Psalm 97.8.]
Nevertheless, I hear that those who have taken up the godless heresy of Eunomius are putting forward a certain Quintianus and the boasted influence they themselves possess at court, to the end that they may again sully the Church; and that certain false teachers are spreading their nets for the souls of weaker brethren. These are the very ones whom the acolytes of Quintianus recently landed upon our shores, and for this very purpose. Their litigation is merely a cloak for their impiety, or even worse, a struggle on behalf of their impiety.
 An adulterous generationnote[Matthew 16.6.] are these elders, modern apostles of the devil and Quintianus. Beware lest they privily attack the flock you are shepherding. Beware lest they privily sow tares amidst your wheat.note[Matthew 13.25.]Their lairs are well known to all. You know well what estates harbor them, you know what houses are open to these bandits. Purse these brigands, nosing out their trail. Seek eagerly for yourselves the blessing that Moses invoked on those who armed themselves, heart and hand against traitors in the camp.note[Numbers 25.10-13.] And this, my brethren, is a thing worth saying to you: 'Let the honorable be honorably done.'
 I counsel you to let all struggle for lucre be put aside, let all be undertaken for God alone; it were ill indeed that virtue and vice should rest on the same foundation. The race is for holiness; we must struggle for men's souls, that no one may plunder them from the Church, as these men have too successfully done in the past. He who governs the Church only to make his own purse heavier, and who be seeming useful in times which call for astuteness, builds up power for himself thereby, that man is one that we must sever from all communion with Christians.
 God has not made Virtue other than perfect; it needs not evil as an ally. Soldiers worthy of churches will never be lacking to God. He will find allies for the cause, unrewarded here below, but fully rewarded in Heaven. Be ye of their number. It is quite as just to curse evildoers as it is to pray with those that walk uprightly. Whosoever weakens and betrays his cause, and whosoever comes forward in it only to lay his hands on another's possessions, may such an one never be sinless in the eyes of God.
 Make this alone your cardinal point, therefore, to circumvent these evil bankers who adulterate the divine decree as if it were coin. Make all see them in their true light, and thus have them disfranchised and banished from the frontiers of Ptolemais, taking whatever they brought with them, unweighed. Whosoever shall act contrary to these instructions, may he be accursed before God.
 If perchance someone there may be who has seen a nefarious meeting and overlooked the matter, or pretends not to have heard what he has heard, or who even allows himself to be corrupted by baser gain at their hands, anyone of these men we order to be put under such ban as was ordained in the case of the Amalekites, from whom it is not lawful to carry of spoils, and of him who takes them God say, 'I repent me that I made Saul king'.note[1 Samuel 15.11.] May He never have to repent that any of you are his. Be ye all devoted to the service of God, that he may care for us.