By way of leading up to his proof that Christ is not different from the Father, St. Ambrose cites the more famous leaders of the Arian party, and explains how little their witness agrees, and shows what defence the Scriptures provide against them.
43. The Arians, then, say that Christ is unlike the Father; we deny it. Nay, indeed, we shrink in dread from the word. Nevertheless I would not that your sacred Majesty should trust to argument and our disputation. Let us enquire of the Scriptures, of apostles, of prophets, of Christ. In a word, let us enquire of the Father, Whose honour these men say they uphold, if the Son be judged inferior to Him. But insult to the Son brings no honour to the good Father. It cannot please the good Father, if the Son be judged inferior, rather than equal, to His Father.
44. I pray your sacred Majesty to suffer me, if for a little while I address myself particularly to these men. But whom shall I choose out to cite? Eunomius? or Arius and Aëtius, his instructors? For there are many names, but one unbelief, constant in wickedness, but in conversation divided against itself; without difference in respect of deceit, but in common enterprise breeding dissent. But wherefore they will not agree together I understand not.
45. The Arians reject the person of Eunomius, but they maintain his unbelief and walk in the ways of his iniquity. They say that he has too generously published the writings of Arius. Truly, a plentiful lavishing of error! They praise him who gave the command, and deny him who executed it! Wherefore they have now fallen apart into several sects. Some follow after Eunomius or Aëtius, others after Palladius or Demophilus and Auxentius, or the inheritors of this form of unbelief. Others, again, follow different teachers. Is Christ, then, divided? Nay; but those who divide Him from the Father do with their own hands cut themselves asunder.
46. Seeing, therefore, that men who agree not among themselves have all alike conspired against the Church of God, I shall call those whom I have to answer by the common name of heretics. For heresy, like some hydra of fable, has waxed great from its wounds, and, being ofttimes lopped short, has grown afresh, being appointed to find meet destruction in flames of fire. Or, like some dread and monstrous Scylla, divided into many shapes of unbelief, she displays, as a mask to her guile, the pretence of being a Christian sect, but those wretched men whom she finds tossed to and fro in the waves of her unhallowed strait, amid the wreckage of their faith, she, girt with beastly monsters, rends with the cruel fang of her blasphemous doctrine.
47. This monster's cavern, your sacred Majesty, thick laid, as seafaring men do say it is, with hidden lairs, and all the neighbourhood thereof, where the rocks of unbelief echo to the howling of her black dogs, we must pass by with ears in a manner stopped. For it is written: “Hedge your ears about with thorns;” and again: “Beware of dogs, beware of evil workers;” and yet again: “A man that is an heretic, avoid after the first reproof, knowing that such an one is fallen, and is in sin, being condemned of his own judgment.” So then, like prudent pilots, let us set the sails of our faith for the course wherein we may pass by most safely, and again follow the coasts of the Scriptures.
Source: On the Christian Faith (De fide) (New Advent)