2 Yet we do not rest, like sailors, on uncertain or on idle hopes: whom, as they shape their course to their wish, and not by assured knowledge, at times the shifting, fickle winds forsake or drive from their course. But we have by our side the unfailing Spirit of faith, abiding with us by the gift of the Only-begotten God, and leading us to smooth waters in an unwavering course. For we recognise the Lord Christ as no creature, for indeed He is none such; nor as something that has been made, since He is Himself the Lord of all things that are made; but we know Him to be God, God the true generation of God the Father.
All we indeed, as His goodness has thought fit, have been named and adopted as sons of God: but He is to God the Father the one, true Son, and the true and perfect birth, which abides only in the knowledge of the Father and the Son. But this only, and this alone, is our religion, to confess Him as the Son not adopted but born, not chosen but begotten. For we do not speak of Him either as made, or as not born; since we neither compare the Creator to His creatures, nor falsely speak of birth without begetting. He does not exist of Himself, Who exists through birth; nor is He not born, Who is the Son; nor can He, Who is the Son, come to exist otherwise than by being born, because He is the Son.
Source: On the Trinity (New Advent)