Men who now speak of a trinity say that three hypostases may still be One when they perform one and the same operation. Thus declares Gregory Nyssen:

“In the case of the Divine nature we do not learn that the Father does anything by Himself in which the Son does not work conjointly, or again that the Son has any special operation apart from the Holy Spirit; but every operation which extends from God to [Creation]… has its origin from the Father, and proceeds through the Son, and is perfected in the Holy Spirit.” (Ad Ablabium).

Says Gregory also:

“No operation is separated in respect of the Persons… but every providence, care and superintendence of all, alike of the things in the sensible creation and of those of supramundane nature… is one, and not three, being indeed directed by the Holy Trinity, yet not severed by a threefold division according to the number of the Persons.” (Ad Ablabium).

So, he deems the operations of the divine nature to be inseparable, and concludes from this that the essence itself must be without plurality; that because the Father, Son and Spirit act with one and the same motion toward all things, their being must likewise be one and the same.

I answer that this is a categorical mistake, since Gregory has wrongly equated the functional harmony of agents, (proper to one essence) with that true, simple, unity. We do not deny, as you presume, that one essence should be capable of subsisting in three persons, or manifesting itself through diverse operations; However, we do confess that wherever an operation is through a distinction of persons, there is also implied a distinction in agency. And I say, therefore, that Gregory, in saying that each hypostasis has its own unique operation, proceeding in order from Father, to Son, to Spirit, has thereby defined the hypostases—in their being distinct from one another—as agents. And where multiple agents work conjointly, be it perfectly, in the case of the hypostases, or imperfectly, in the case of the souls, there is always plurality. We know that, in order for the plurality to be in harmony, there must be one higher unity governing them. Every complex unity therefore depends on a simpler principle above it.

If, as Gregory writes, each divine operation is sequential through the Father and the Son and the Holy Spirit, then it seems to me that the unity has been ordered within itself. Yet wherever there is order, however it be conceived, there is also relational priority and dependence, which are impossible for the One. For those hypostases must have been given order and priority by that which is higher, that One above all.

So it is with the Soul, which is one in essence (ousia) but plural in activity (energeiai). For though all men partake of one and the same rational nature, their activities are diverse and often contrary. So too, if even the soul’s unity of essence allows plurality of action, how much less can multiple divine agents, however perfectly harmonious, constitute true unity? Again, the essence of the soul is single. It is reason and life itself. Because it is incorporeal, its being cannot be divided; for incorporeal things admit not partition of being, but are one. However, it is not therefore a single agent. Behold: each man’s soul acts according to its own disposition, but the unity of the Universal Soul in essence does not abolish the plurality of activity within our own individual souls. Indeed, were it possible for all human souls to act harmoniously—in other words, every mind willing, thinking and judging without contradiction—that harmony of souls would not make them truly One, rather would they become a reflection of that higher order of unity above them. For indeed, the perfect coordination of many agents retains plurality in operation, though imitating the simplicity of That which is truly One.

Consider the chorus in the theatre. You hear many voices singing the same song, as long as the conductor is cuing the singers. The unity of those singers, however it may appear, has not its origins in them, but in that conductor conducting them. Should the conductor cease his conducting, all the voices would immediately diverge, that apparent unity dissolving thereby. In this sense, the harmony of their song is participatory, not essential. And, this can be said of all orders where there is harmonization of plurality. The unity in the order of plurality is not self-existent, but contingent upon a higher unity.

Therefore, a triadic operation cannot consist within an absolute unity; rather wherever there are many who act as one, their unity is borrowed. An image only of simplicity, and not simplicity itself. What the Trinitarians have testified testifies to the higher, monadic source of All. For the One, neither acting nor being acted upon, is indeed before all action, and the source of the procession of all harmony.