22 But this wild talk must cease; the rhetoric of exposing heretical folly must give place to the drudgery of framing arguments. So, I trust, those among them who are capable of being saved will set their faces towards the true faith taught by the Evangelists and Apostles, and recognise Him Who is the true Son of God, not by adoption but by nature. For the plan of our reply must be that of first proving that He is the Son of God, and therefore fully endowed with that Divine nature in the possession of which His Sonship consists.
For the chief aim of the heresy, which we are considering, is to deny that our Lord Jesus Christ is true God and truly the Son of God. Many evidences assure us that our Lord Jesus Christ is, and is revealed to be, God the Only-begotten, truly the Son of God. His Father bears witness to it, He Himself asserts it, the Apostles proclaim it, the faithful believe it, devils confess it, Jews deny it, the heathen at His passion recognised it. The name of God is given Him in the right of absolute ownership, not because He has been admitted to joint use with others of the title.
Every work and word of Christ transcends the power of those who bear the title of sons; the foremost lesson that we learn from all that is most prominent in His life is that He is the Son of God, and that He does not hold the name of Son as a title shared with a widespread company of friends.
Source: On the Trinity (New Advent)