9 The honest repudiation of Arianism involves the acceptance of the Nicene test.
This then the Fathers perceived when they wrote that the Son was coessential with the Father, and anathematised those who say that the Son is of a different Subsistence: not inventing phrases for themselves, but learning in their turn, as we said, from the Fathers who had been before them. But after the above proof, their Ariminian Synod is superfluous, as well as any other synod cited by them as touching the Faith. For that of Nicæa is sufficient, agreeing as it does with the ancient bishops also, in which too their fathers signed, whom they ought to respect, on pain of being thought anything but Christians. But if even after such proofs, and after the testimony of the ancient bishops, and the signature of their own Fathers, they pretend as if in ignorance to be alarmed at the phrase 'coessential,' then let them say and hold, in simpler terms and truly, that the Son is Son by nature, and anathematise as the synod enjoined those who say that the Son of God is a Creature or a thing made, or of nothing, or that there was once a time when He was not, and that He is mutable and liable to change, and of another Subsistence. And so let them escape the Arian heresy. And we are confident that in sincerely anathematising these views, they ipso facto confess that the Son is of the Father's Essence, and coessential with Him. For this is why the Fathers, having said that the Son was coessential, straightway added, 'but those who say that He is a creature, or made, or of nothing, or that there was once a time when He was not,' the Catholic Church anathematises: namely in order that by this means they might make it known that these things are meant by the word 'coessential.' And the meaning 'Coessential' is known from the Son not being a Creature or thing made: and because he that says 'coessential' does not hold that the Word is a Creature: and he that anathematises the above views, at the same time holds that the Son is coessential with the Father; and he that calls Him 'coessential,' calls the Son of God genuinely and truly so; and he that calls Him genuinely Son understands the texts, 'I and the Father are one,' and 'he that has seen Me has seen the Father. '
Source: Ad Afros Epistola Synodica (New Advent)