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:

ㅤ

ㅤ

“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 considers the operations of the divine nature to be inseparable, while also holding that the divine essence is simple; that because they act by the same motion toward all things, their being also is one and the same.

I answer that this is a categorical mistake, since Gregory has wrongly equated the unity of operation among distinct hypostases with that true, simple, unity. We do not, as you presume, deny that one essence should be able to subsist in three persons, or manifest in diverse operations; However, we do confess that whenever one operation proceeds through a real distinction of persons, there is a distinction within the agency. And I say, therefore, that Gregory, in saying that the one operation proceeds in order from Father, through Son, to Spirit, has in this distinguished the hypostases within that agency. If these hypostases are indeed distinct from each other, and yet they should be said to effect the same operation together, then their plurality will not be abolished by merely claiming the inseparability of their action. 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. That is to say, there remains a numerical plurality of agents.

If, as Gregory writes, each divine operation proceeds in order from the Father, through the Son and to the Holy Spirit, then it seems to me that this is a unity which has been ordered within itself. Yet wherever there is order, however it be conceived, there is also relation of origin and priority (for Gregory so vainly says that the Father is Cause and the Son caused), which is to say, a type of plurality, which for the One is impossible. For those hypostases, which belong to the order of plurality as we have established, must derive their order and unity from that which is higher, namely, 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 distinct hypostases, however perfectly harmonious in operation, be called a 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 agency, though imitating (through participation) the simplicity of That which is truly One.

Consider the chorus in the theater. You hear many voices singing the same song, as long as the conductor is cuing the singers. The unity of those singers, however perfect it may appear, has not its origins in them, but in that conductor conducting them. Should the conductor cease his conducting, all the voices may 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 must be contingent upon a higher unity, and even otherwise, cannot be called the absolute simplicity of the One.

Therefore, a triadic agency cannot subsist 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.