De Synodis 43

III. "And if any one hearing that the Only-begotten Son is like the invisible God, denies that the Son who is the image of the invisible God (whose image is understood to include essence) is Son in essence, as though denying His true Sonship: let him be anathema." 15. It is here insisted that the nature is indistinguishable and entirely similar. For since He is the Only-begotten Son of God and the image of the invisible God, it is necessary that He should be of an essence similar in species and nature. Or what distinction can be made between Father and Son affecting their nature with its similar genus, when the Son subsisting through the nature begotten in Him is invested with the properties of the Father, viz., glory, worth, power, invisibility, essence? And while these prerogatives of divinity are equal we neither understand the one to be less because He is Son, nor the other to be greater because He is Father; since the Son is the image of the Father in species, and not dissimilar in genus; since the similarity of a Son begotten of the substance of His Father does not admit of any diversity of substance, and the Son and image of the invisible God embraces in Himself the whole form of His Father's divinity both in kind and in amount: and this is to be truly Son, to reflect the truth of the Father's form by the perfect likeness of the nature imaged in Himself.