46 This is no universal and inevitable error; they who deny the Son cannot lay the fault upon their ignorance, for ignorance of the truth which they deny is impossible. They describe the Son of God as a creature who came into being out of nothing. If the Father has never asserted this, nor the Son confirmed it, nor the Apostles proclaimed it, then the dating which prompts their allegation is bred not of ignorance, but of hatred for Christ. When the Father says of His Son, This is, and the Son of Himself, It is He that talks with You, and when Peter confesses You are, and John assures us, This is the true God, and Paul is never weary of proclaiming Him as God's own Son, I can conceive of no other motive for this denial than hatred.
The plea of want of familiarity with the subject cannot be urged in extenuation of their guilt. It is the suggestion of that Evil One, uttered now through these prophets and forerunners of his coming; he will utter it himself hereafter when he comes as Antichrist. He is using this novel engine of assault to shake us in our saving confession of the faith. His first object is to pluck from our hearts the confident assurance of the Divine nature of the Son; next, he would fill our minds with the notion of Christ's adoption, and leave no room for the memory of His other claims.
For they who hold that Christ is but a creature, must regard Christ as Antichrist, since a creature cannot be God's own Son, and therefore He must lie in calling Himself the Son of God. Hence also they who deny that Christ is the Son of God must have Antichrist for their Christ.
Source: On the Trinity (New Advent)