One of the stumbling blocks moderns face when they engage with classical trinitarian theology is that the main stream of the tradition resolutely affirms that there is one will in God; that is, one divine will that belongs to the divine nature. It follows from this that Father, Son, and Holy Spirit do not have three wills, but one.
The reason this is difficult for modern readers is that moderns instinctively associate will with person. If that association (will goes with person) were to be axiomatic, then it would indeed follow that there are three wills in God. Fair enough; at this point we might ask what the grounds are for counting wills with persons, and then of course we’d have to offer at least a rough draft of a definition of will before going any further. Good work worth doing; clarity clarity ah what a rarity, and so on.
But another angle worth taking on the issue is to inquire into the shift that happened in our habits of association somewhere between ancient and modern. Somewhere around the eighteenth century, the presuppositions or plausibility structures about personhood were somehow altered. This happened in the broader intellectual culture and then moved into theology proper from there; I mention that not to discredit the change, but to point out that for theological thinking, the shift avoided direct scrutiny because it was a background issue that didn’t draw attention as it was happening. Especially in English-language divinity, when the new notion of personhood hit Trinitarianism it created lots of confusion and turbulence. See Dixon’s Nice & Hot Disputes (2006) and Lim’s Mystery Unveiled (2012) for detailed discussion of the concept of personhood. One of the hardest things about reading trinitarian theology from about 1700 on is that you can never tell in advance which theologians have noticed the shift and have adjusted their way of talking accordingly. As a result, these theologians can be quoted on both sides of many vexed questions (think of social trinitarian issues, or detailed accounts of the eternal relation between Father and Son).
Once you do attend to this shift, from associating will with a shared nature to associating it with individual people, it may seem that there is a decision to make: should I think in pre-shift categories, or post-shift? You might choose pre-shift categories just to maintain frictionless alignment with the ancient church; or you might choose post-shift categories just to give priority to clear communication with your contemporaries. But here’s an argument for prioritizing the pre-shift way of organizing your thought.
In the fourth century, Eunomius made a case for subordinationism (think of Eunomianism as a kind of rationalistic, third-wave Arianism). He had a clever argument that went like this: The Father must have generated the Son either willingly or unwillingly. He intended this as a dichotomy that would eliminate the notion of eternal generation. If the Father generated the Son by an act of his will, then the Son was a creature that the Father chose to bring forth. But if the Father generated the Son against his own will, then the Father was himself demoted from Godhood because he was under compulsion by something greater. Since the latter was impossible (Eunomius did at least try to champion a high view of the transcendent first principle), the truth must be the former: that the Son is a creature.
Gregory of Nazianzus rejected the terms of the dichotomy, in the fourth of his Five Theological Orations. According to Gregory, the Father generates the Son neither willingly nor unwillingly, but by nature. To equip the Father with a personal will distinct from the Son would be to remove the Son from the divine nature in advance. But pro-Nicene theology insisted that there never was a divine will that was not the will of the Father and the Son. Athanasius in fact had already preemptively refuted the logic of the Eunomian move in his Contra Arianos. The Son, he argued, is not produced by the goodwill (eudokia) of the Father, but is himself that goodwill.* The Father was never without goodwill, but always had his goodwill with him. It’s the same argument Athanasius makes about the Father’s logos; it trades on logos being both integral to the Father’s own identity and also an eternal counterpart to the Father (you might say psychological and social analogies respectively).
In my opinion, that pro-Nicene move is the deep logic that dictates why, when thinking theologically, we should prioritize the association of will with nature. It’s grounded in the unity of the Trinity and the character of eternal generation. We can take that as the foundational move (for dogmatic ordering) and then give due attention to communicating clearly with contemporaries.
Of course, if you treat a will as a separable psychological faculty and ask whether it belongs to a divine person or the divine nature, it fits neither category cleanly. If you put it into the person (and say there are three such in God) then you move the Son out of the divine unity and have to explain whether the Father generated him willingly or unwillingly: back to Eunomius. But if you put it in nature, then you suggest that the singular divine nature is the real agent/willer/person in God. In other words, subordinationism looms on one side and modalism on the other. It may help some to specify that you’re talking about a “natural will,” that is, what a nature tends toward as such. This line of discussion gets developed in the conciliar doctrine of the incarnation when Christ is confessed to have two wills: the will of the eternal divine nature, and the will of the assumed human nature. It may also be helpful to use “energies” as a kind of bridge term, as Maximus and the conciliar tradition did: each nature has natural energies, the incarnate Son has both energies, and blending them into one would be an error called monoenergism.
I’m sure I’m leaving out some steps in the argument here, but it seems to me that if you come to this question “from above,” that is, from the clear guidelines of the pro-Nicene argument, it not only helps you avoid being misled by the way words get used with different meanings before and after the shift, but also establishes some guiding limits about how much you can apply the modern definition of person (center of consciousness with its own independent stream of mental contents and series of volitions, etc.) to the Father, Son, and Spirit.
*Note to self for future research: Track Patristic use of eudokia in a trinitarian context. Start with the entry in Lampe’s Patristic Greek Lexicon.