In Against Eunomius I.1.34 (NPNF 5), Gregory says this regarding the Father and Son sharing in one nature:
So also the Father and Son are one, the community of nature and the community of will running, in them, into one. But if the Son had been joined in wish only to the Father, and divided from Him in His nature, how is it that we find Him testifying to His oneness with the Father, when all the time He was sundered from Him in the point most proper to Him of all?
At first glance this sounds problematic from the standpoint of proponents of dyothelite Christology and, correspondingly, one will in the Godhead. A phrase like “community of wills,” along with the analogy Gregory uses right before this of two men agreeing with one another, could be taken to mean that Nyssen is here implicitly affirming multiple divine wills. This is, in fact, just the kind of passage that twentieth-century social Trinitarians might point to in favor of their understanding of “person,” and in fact the Cappadocians are employed frequently in support of their position. But there are clear reasons to reject a “social Trinitarian” reading of Gregory, at least in this particular passage.
1. Elsewhere in Nyssen, as well as in other pro-Nicenes, God is one in every way. The *only* distinction that exists in the Godhead is the means of subsistence in the essence, i.e. the eternal relations of origin that distinguish the persons. Nyssen previously in “Against Eunomius” has spoken repeatedly of the fact that God is one in every conceivable way – power, authority, command, goodness, justice, glory, etc. The only way that the persons are distinguished is via eternal relations of origin (see e.g. I.1.22).
2. The context clearly affirms one will. Nyssen speaks immediately prior to this passage about God’s will in the singular. Again, this is in accord with the way Nyssen speaks elsewhere about God’s simple unity.
3. The analogy with the two men agreeing is not intended to be one to one correspondence. Nyssen makes this quite clear throughout his works on the Trinity, including “Against Eunomius.” We should not take his analogy here as anything more than that – analogous. Nyssen consistently affirms a healthy dose of apophaticism and the analogical nature of language elsewhere.
4. The syntax of the sentence makes clear that Gregory does not mean multiple wills in the Godhead. Here it is in Greek:
καὶ ὁ πατὴρ καὶ ὁ υἱὸς ἕν εἰσι, τῆς κατὰ τὴν φύσιν καὶ τὴν προαίρεσιν κοινωνίας εἰς τὸ ἓν συνδραμούσης
Note both clauses. The first clause has two singular nouns (“father” and “son”) taking a plural verb to describe them (“are”), but the predicate noun is singular. The plural persons of Father and Son are one. Of course, this is no different than Jesus’ affirmation in John 17. What about the second clause, the more troubling one for our purposes? To begin with, this is an explanatory clause about how Father and Son are one, as indicated by the κατὰ preposition. So Nyssen is at the very least not contradicting his previous statement, but expanding on it. When we look at this expansion of his explanation about God’s oneness, we find two singular nouns – “nature” and “will” – in the middle of a genitive absolute clause – τῆς … κοινωνίας. In other words, whatever “community” means here, it is defined according to (κατὰ) both nature and will. (I am dependent on Seumas Macdonald for insights into the syntax of this sentence). Nyssen is certainly not positing a “community of natures” in the way a “community of wills” would have to be taken for trithelitism. In fact, all that Nyssen really seems to mean here is that, while distinct in their personhood, Father and Son are one in essence and volition.
This, by the way, is the problem with “proof-texting” the Fathers. If one simply presses CTRL-F for “will,” several passages like this will pop up. If we read them cursorily and out of context, they seem to support a social Trinitarian view of the divine persons. But on further inspection, that could not be further from the truth.