St. Ambrose deprecates any praise of his own merits: in any case, the Faith is sufficiently defended by the authoritative support of holy Scripture, to whose voice the Arians, stubborn as the Jews, are deaf. He prays that they may be moved to love the truth; meanwhile, they are to be avoided, as heretics and enemies of Christ.
129. These arguments, your Majesty, I have set forth, briefly and summarily, in the rough, rather than in any form of full explanation and exact order. If indeed the Arians regard them as imperfect and unfinished, I indeed confess that they are scarce even begun; if they think that there be any still to be brought forward, I allow that there be nearly all; for whereas the unbelievers are in uttermost need of arguments, the faithful have enough and to spare. Indeed, Peter's single confession was abundant to warrant faith in Christ: “You are the Christ, the Son of the living God;” for it is enough to know His Divine Generation, without division or diminution, being neither derivation nor creation.
130. This, indeed, is declared in the books of Holy Writ, one and all, and yet is still doubted by misbelievers: “For,” as it is written, “the heart of this people has become gross, and with their ears they have been dull of hearing, and their eyes have they darkened, lest ever they should see with their eyes, and hear with their ears, and understand in their heart.” For, like the Jews, the Arians' wont is to stop their ears, or make an uproar, as often as the Word of salvation is heard.
131. And what wonder, if unbelievers doubt the word of man, when they refuse to believe the Word of God? The Son of God, as you will find it written in the Gospel, said: “Father, glorify Your Name,” and from heaven was heard the voice of the Father, saying: “I have both glorified it, and again will glorify.” These words the unbelievers heard, but believed not. The Son spoke, the Father answered, and the Jews said: “A peal of thunder answered Him;” others said: “An angel spoke to Him.”
132. Paul, moreover, as it is written in the Acts of the Apostles, when by the Voice of Christ he received the call of grace, several companions journeying with him at the same time, alone said that he had heard Christ's Voice. Thus, your sacred Majesty, he who believes, hears— and he hears, that he may believe, while he who believes not, hears not, nay, he will not, he cannot hear, lest he should believe!
133. As for me, indeed, would that they might have a will to hear, that they might believe— to hear with true love and meekness, as men seeking what is true, and not assailing all truth. For it is written that we pay no heed to “endless fables and genealogies, which do rather raise disputes than set forward the godly edification, which is in faith. But the aim of the charge is love from a pure heart, and a good conscience, and faith unfeigned, whence some have erred and betaken themselves to empty babbling, desirous of being teachers of the law, without understanding the words they say, nor the things whereof they speak with assurance.” In another place also the same Apostle says: “But foolish and ignorant questionings do thou avoid.”
134. Such men, who sow disputes— that is to say, heretics— the Apostle bids us leave alone. Of them he says in yet another place, that “certain shall depart from the faith, giving heed to deceitful spirits, and the doctrines of devils.”
135. John, likewise, says that heretics are Antichrists, plainly marking out the Arians. For this [Arian] heresy began to be after all other heresies, and has gathered the poisons of all. As it is written of the Antichrist, that “he opened his mouth to blasphemy against God, to blaspheme His Name, and to make war with His saints,” so do they also dishonour the Son of God, and His martyrs have they not spared. Moreover, that which perchance Antichrist will not do, they have falsified the holy Scriptures. And thus he who says that Jesus is not the Christ, the same is Antichrist; he who denies the Saviour of the world, denies Jesus; he who denies the Son, denies the Father also, for it is written; “Every one which denies the Son, denies the Father likewise.”
Source: On the Christian Faith (De fide) (New Advent)