Gregory of Nazianzus tried to explain how there could be both a Father and a Son in a God who was supposedly not only One, but eternal. "When did these come into being? They are above all 'When'" (58). Gregory explained that time is irrelevent to God, who is beyond time. "there never was a time when He was not" (58). In this argument, because of the Father's unoriginate nature, anything originated from this Father (the Son and the Holy Spirit) are also eternal. With the use of several other mind-bending ideas about time and eternity, as well as the nature of the Father, Gregory of Nazianzus turns the argument of this begotten God into a question of faith: "It was in a manner known to the Father Who begat, and to the Son Who was begotten. Any more than this is hidden by a cloud, and escapes your dim sight" (59). That is to say, we as humans can never fully comprehend the nuances of God's nature.
Gregory of Nyssa seems to believe the nature of the Trinity CAN be explained, and to do so, he uses human nature in comparisson. He argues that "man" is an all encompassing term for human beings, who may be seperate, just as "God" is an all encompassing term for the nature of the three: Father, Son, Holy Spirit. "...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 the Creation...has its origin from the Father, and proceeds through the Son, and is perfected in the Holy Spirit" (62). This is an example compared to a committee of men working on a project. They are united by the same goals (or seperated by misunderstanding). Gregory of Nyssa concludes that each member of the Trinity is indeed God "because no difference either of nature or of operation is contemplated in the Godhead" (62), which means that they are all of the same nature, that of God, and they are united by whatever goals they may have for Creation.
These arguments are both valid. But they also prove the same point: That it is impossible to explain the Trinity. While this seemed to be Gregory of Nazianzus' original intent, it was obviously not Gregory of Nyssa's. The latter intended to prove something about God in his treatise, but his methods were faulty. He tried to explain God through humanity, which is impossible. There is no possible comparisson between God and humans, being that they are two completely different beings: God eternal, humans mortal. God omnipotent, humans struggling to understand their lives. Gregory of Nyssa's argument was flawed from the beginning. Gregory of Nazianzus, however, had a better grasp on the nature of God. His whole argument was based around the fact that there is no way we as humans could understand the Trinity, it's nature, and eternity. Both arguments ultimately stated that the Trinity is unexplainable.
I would be more inclined to follow the line of thinking that Gregory of Nazianzus presented, which says that comprehension of the Trinity is impossible. It stands to reason that a being so unfathomable could ever be understood. Any attempts to do so would probably result sounding like a fool. This is what Gregory of Nyssa does to me: He sounds like a fool. Obviously, three human beings are just that, three human beings. They are seperate creatures, regardless of sharing human nature or a common goal. They are not, never were, and never will be the same person. They came from different parents. Attempting to explain a being that is One of Three by using human models is defective. So, with all of his ramblings, Gregory of Nyssa only proved that he knows very little about the nature of God.