In the mid-fourth century A.D., Ablabius, a Christian and Roman official from Crete, wrote on the Trinity, posing some fascinating questions about the nature of the Godhead. Bishop Gregory of Nyssa responded to Ablabius in his work, On “Not Three Gods.” Here is how Gregory paraphrases Ablabius’ question:
The argument which you state is something like this:—Peter, James, and John, being in one human nature, are called three men: and there is no absurdity in describing those who are united in nature, if they are more than one, by the plural number of the name derived from their nature. If, then, in the above case, custom admits this, and no one forbids us to speak of those who are two as two, or those who are more than two as three, how is it that in the case of our statements of the mysteries of the Faith, though confessing the Three Persons, and acknowledging no difference of nature between them, we are in some sense at variance with our confession, when we say that the Godhead of the Father and of the Son and of the Holy Ghost is one, and yet forbid men to say “there are three Gods”? 
Here’s another way to put it:
- Peter, James, and John all share the same human nature and have distinct names.
- We refer to them in the plural as men.
- The Father, the Son, and the Holy Spirit share the same divine nature and have distinct names.
- We do not refer to them in the plural as gods.
Even Gregory admits, this is a difficult question! However, he goes on to address it so that we may “no longer totter and waver in this monstrous dilemma.”
Gregory first posits that our speaking of “many men” in relation to human nature is an “abuse of language.” What we really mean to say in the above scenario with Peter, James, and John is that there are three instances of one nature, not three natures. Perhaps Gregory would be better pleased if we said “three persons” rather than “three men.”
He moves on to address the term “Godhead” and demonstrates that it refers to operation, not nature. Because the Father does not do any action without the aid of the Son and the Spirit, we do not divide according to the number of persons doing the work. “[T]he action of each concerning anything is not separate and peculiar, but whatever comes to pass, in reference either to the acts of His providence for us, or to the government and constitution of the universe, comes to pass by the action of the Three, yet what does come to pass is not three things.”
Keith E. Johnson, in his excellent article in Themelios (Volume 36, Issue 1), rightly points out that this is not a new refrain; Gregory does not stand alone, but alongside Church Fathers such as Augustine and Athanasius. “That the divine persons act inseparably ad extra according to their relative properties ad intra is an assumption Augustine shares not only with the entire Latin pro-Nicene tradition but also the Greek-speaking theologians of the East”
Near the end of this work, Gregory admits that his argument would fall if one were to suppose that the Godhead denotes nature rather than operation. However, he is then quick to fall back humbly on the words of Scripture, “Hear, O Israel: The Lord our God, the Lord is one” (Deuteronomy 6:4). Ultimately our faith rests not on human polemics, but on the steadfast Word of God.
Read the rest of Gregory’s treatise in response to Ablabius in the Nicene and Post-Nicene Fathers, along with other helpful works on the Trinity, such as Basil’s Against Eunomius, Athanasius’ Letters to Serapion, and Augustine’s famous De Trinitate. Get the whole set in Logos today!
 Gregory of Nyssa, “On ‘Not Three Gods’,” in A Select Library of the Nicene and Post-Nicene Fathers of the Christian Church, Second Series: Gregory of Nyssa: Dogmatic Treatises, Etc., ed. Philip Schaff and Henry Wace, trans. Henry Austin Wilson, vol. 5 (New York: Christian Literature Company, 1893), 331.
 Ibid., 334.
 Keith E. Johnson, “Trinitarian Agency and the Eternal Subordination of the Son: An Augustinian Perspective,” Themelios, No. 1, April 2011 36 (2011): 17.