18. The Catholic Faith confesses that the 'properties' of the Persons are identical with the Persons themselves; and that the Persons themselves are nothing else than one God, one Divine Substance, one Divine Nature, one Divine and Supreme Majesty. Number, therefore, if you can, either the Persons without the Substance, which they themselves are, or the characteristics without the Persons with whom they are identical. Or, if any one endeavour to separate the Persons from the Substance, or the characteristic attributes from the Persons, I am at a loss to understand how he can profess to be a worshipper of the Trinity after dividing the Godhead into such a vast multitude of particulars. Let us therefore maintain that there are three Persons, but not to the prejudice of the Unity : let us hold that there is one God, but not so as to confound the Trinity ; for these are not mere names, nor idle words void of meaning. If any one asks how this can be, let him be content to hold that it is so, though I must add that if the doctrine be not clear to reason, it is no halting opinion, but the firm conviction of faith. This is a great mystery, worthy of all veneration, not to be keenly scrutinized. How can plurality consist with unity, or unity with plurality ? To closely examine the fact is rashness, to believe it is piety, to know it is life, and eternal life. Wherefore, Eugenius, if you think it worth while, let me have your undivided consideration as I run through the many arguments which tend to show the greatness of this unique unity. There is a unity which we may call ‘collective’, as, for example, when many stones make one heap. There is a ‘constitutive’ unity, as when many members make one body, or many parts constitute one whole. There is a unity such as that of man and wife, whereby two are no longer two, but one flesh. And there is a ‘natural’ unity, whereby soul and body are one man. There is a ‘potential’ unity, the realization of which is the constant endeavour of a virtuous man, so that he may not be unstable, nor unlike himself. There is the unity of agreement, when the love of many men leads to their being of one heart and one soul. There is also the unity of devotion, when the soul, cleaving to God with complete surrender, is one spirit. And there is the unity of condescension, whereby our poor nature was taken by the Word of God to make one person in Himself.
19. But what are all these compared with that supreme, and, so to speak, unique unity which results from the consubstantiality of the three Persons? If you find a likeness between any one of the foregoing and this unity, the resemblance is but partial; if you compare them with it, there will be no true resemblance. Therefore, among all things which are rightly called 'One', the unity of the Trinity, whereby three Persons are one Substance, is the highest. Next comes that surpassing unity, whereby, conversely, three substances are in Christ, one Person. Moreover, real sober consideration proves that the foregoing, and whatsoever else can be called 'One', have the title in virtue of their resemblance to that supreme Unity, not because they allow of comparison therewith. Nor do we forsake this profession of the Unity by our upholding of the doctrine of the three Persons, since, when we speak of the Trinity, we do not mean a multiplicity of gods any more than in speaking of unity we imply loneliness. Wherefore, when I speak of One I am not disturbed by the consideration of number, which does not multiply the essence, nor change it, nor divide it. Again, when I speak of three things, if I view them as one, whatever the three things may be, I am not proved wrong. Nor, if I speak of the three Persons of the Godhead, am I obliged to confound the Persons, or reduce the three to the One.