Some folks like to paint Gregory of Nyssa as though he were a Roman Catholic. Certainly, of course, there are points where his theology contains errors. His beliefs would not have squared with the Westminster Confession of Faith in every respect. So, to be clear, Gregory of Nyssa was neither a "Roman Catholic" nor a "Reformed Presbyterian." He was an early churchman, and more specifically a Cappadocian.
One area where we can see his similarity to the Reformed camp and difference from the Roman camp is on the issue of the supposed immaculate conception of Mary. Like many of the church fathers, Gregory of Nyssa had no concept of the sinlessness of Mary. The only person Gregory of Nyssa ever describes as "sinless" is Christ, and Gregory viewed Christ as unique in this regard. Let's look at his discussion of that topic.
We next learn about the return of a person who has erred and the change from evil to enjoyment of the good. He [Christ] who has been tempted in all things and is without sin [Heb 4.15] holds converse with us in our human nature. He who assumed our weakness showed us a way out of evil through the infirmities of his human nature. "Instruct me in the Wisdom [Christ] according to the Solomon who was in the flesh which held converse with us." Once familiar with it, we are able to pass judgment on what men pursue.
- Gregory of Nyssa, Commentaries on Ecclesiastes, Second Homily
This is really just a quotation of the Biblical declaration of Christ's sinlessness.
The Christian Faith, which in accordance with the command of our Lord has been preached to all nations by His disciples, is neither of men, nor by men, but by our Lord Jesus Christ Himself, Who being the Word, the Life, the Light, the Truth, and God, and Wisdom, and all else that He is by nature, for this cause above all was made in the likeness of man, and shared our nature, becoming like us in all things, yet without sin.
- Gregory of Nyssa, Against Eunomius, Book II, Chapter 1
Again, this is just a quotation of the Biblical declaration of Christ's sinlessness.
Thus we say that this expression, as well as the other, admits of an orthodox interpretation. For He Who for our sakes became like as we are, was in the last days truly created—He Who in the beginning being Word and God afterwards became Flesh and Man. For the nature of flesh is created: and by partaking in it in all points like as we do, yet without sin, He was created when He became man: and He was created "after God [Ephesians 4:24]," not after man, as the Apostle says, in a new manner and not according to human wont.
- Gregory of Nyssa, Against Eunomius, Book II, Chapter 10
This too is just a quotation of the Biblical declaration of Christ's sinlessness.
Now sin is nothing else than alienation from God, Who is the true and only life. Accordingly the first man lived many hundred years after his disobedience, and yet God lied not when He said, "In the day that you eat thereof you shall surely die." For by the fact of his alienation from the true life, the sentence of death was ratified against him that self-same day: and after this, at a much later time, there followed also the bodily death of Adam. He therefore Who came for this cause that He might seek and save that which was lost, (that which the shepherd in the parable calls the sheep,) both finds that which is lost, and carries home on His shoulders the whole sheep, not its skin only, that He may make the man of God complete, united to the deity in body and in soul. And thus He Who was in all points tempted like as we are, yet without sin, left no part of our nature which He did not take upon Himself. Now the soul is not sin though it is capable of admitting sin into it as the result of being ill-advised: and this He sanctifies by union with Himself for this end, that so the lump may be holy along with the first-fruits.
- Gregory of Nyssa, Against Eunomius, Book II, Chapter 13
Here Christ's sinlessness is used to uniquely identify him. Although Gregory does not explicitly say that there is only one such person, he uses the expression as though it were a particular identifier.
Now if, in becoming Son of Man, he were without participation in human nature, it would be logical to say that neither does He share in the Divine essence, though He is Son of God. But if the whole compound nature of man was in Him (for He was "in all points tempted like as we are, yet without sin" [Hebrews 4:15]), it is surely necessary to believe that every property of the transcendent essence is also in Him, as the Word "Son" claims for Him both alike— the Human in the man, but in the God the Divine.
- Gregory of Nyssa, Against Eunomius, Book III, Chapter 4
This is just another quotation of the Biblical declaration of Christ's sinlessness.
For he everywhere attributes to the Human element in Christ the dispensation of the Passion, when he says, "for since by man came death, by man came also the resurrection of the dead [1 Corinthians 15:21]," and, "God, sending His own Son in the likeness of sinful flesh, condemned sin in the flesh " (for he says, "in the flesh," not "in the Godhead"); and "He was crucified through weakness" (where by "weakness" he means "the flesh"), "yet lives by power [2 Corinthians 13:4]" (while he indicates by "power" the Divine Nature); and, "He died unto sin" (that is, with regard to the body), "but lives unto God [Romans 6:10]" (that is, with regard to the Godhead, so that by these words it is established that, while the Man tasted death, the immortal Nature did not admit the suffering of death); and again; "He made Him to be sin for us, Who knew no sin 2 Corinthians 5:21," giving once more the name of "sin" to the flesh.
- Gregory of Nyssa, Against Eunomius, Book VI, Chapter 1
This passage is interesting in the debate on the atonement with modern Roman Catholics, but as to the issue of Christ's sinlessness, it is simply a quotation of one of the Scriptural affirmations of that fact.
For we give the name of "passion" only to that which is opposed to the virtuous unimpassioned state and of this we believe that He Who granted us salvation was at all times devoid, Who "was in all points tempted like as we are yet without sin [Hebrews 4:15]." Of that, at least, which is truly passion, which is a diseased condition of the will, He was not a partaker; for it says "He did no sin, neither was guile found in His mouth [1 Peter 2:22]"; but the peculiar attributes of our nature, which, by a kind of customary abuse of terms, are called by the same name of "passion,"— of these, we confess, the Lord did partake,— of birth, nourishment, growth, of sleep and toil, and all those natural dispositions which the soul is wont to experience with regard to bodily inconveniences,— the desire of that which is lacking, when the longing passes from the body to the soul, the sense of pain, the dread of death, and all the like, save only such as, if followed, lead to sin.
- Gregory of Nyssa, Against Eunomius, Book VI, Chapter 3
Here Gregory emphasizes Christ's sinlessness with reference to several relevant passages.
Since, then, this was the sum of our calamity, that humanity was exiled from the good Father, and was banished from the Divine oversight and care, for this cause He Who is the Shepherd of the whole rational creation, left in the heights of heaven His unsinning and supramundane flock, and, moved by love, went after the sheep which had gone astray, even our human nature. For human nature, which alone, according to the similitude in the parable, through vice roamed away from the hundred of rational beings, is, if it be compared with the whole, but an insignificant and infinitesimal part. Since then it was impossible that our life, which had been estranged from God, should of itself return to the high and heavenly place, for this cause, as says the Apostle, He Who knew no sin is made sin for us, and frees us from the curse by taking on Him our curse as His own, and having taken up, and, in the language of the Apostle, "slain" in Himself "the enmity" which by means of sin had come between us and God—(in fact sin was "the enmity")— and having become what we were, He through Himself again united humanity to God.
- Gregory of Nyssa, Against Eunomius, Book XII, Chapter 1
This is another passage that is very interesting with respect to the atonement. It also tangentially touches on the theological point that a reason that Christ was a suitable mediator was his sinlessness. But again, as to our particular topic, Gregory is simply reiterating the Scriptural position that Christ had no sin.
"But I do not see," he rejoins, "how God can be above His own works simply by virtue of such things as do not belong to Him." And on the strength of this clever sally he calls it a union of folly and profanity, that our great Basil has ventured on such terms. But I would counsel him not to indulge his ribaldry too freely against those who use these terms, lest he should be unconsciously at the same moment heaping insults on himself. For I think that he himself would not gainsay that the very grandeur of the Divine Nature is recognized in this, viz. in the absence of all participation in those things which the lower natures are shown to possess. For if God were involved in any of these peculiarities, He would not possess His superiority, but would be quite identified with any single individual among the beings who share that peculiarity. But if He is above such things, by reason, in fact, of His not possessing them, then He stands also above those who do possess them; just as we say that the Sinless is superior to those in sin. The fact of being removed from evil is an evidence of abounding in the best. But let him heap these insults on us to his heart's content. We will only remark, in passing, on a single one of the points mentioned under this head, and will then return to the discussion of the main question.
- Gregory of Nyssa, Answer to Eunomius' Second Book
Here Gregory identifies "Sinless" and God, and uses "the Sinless" as a unique designator, even more clearly than in the previous instance above.
He became the image of the invisible God out of love so that in his own form which he assumed, you might be conformed through him to the stamp of archetypal beauty for becoming what he was from the beginning. If we are to become the invisible God's image, we must model the form of our life upon the pattern given us (Jn 13.15). What is this model? He who lives in the flesh does not live according to it (Rom 8.12). That prototype is the image of the invisible God; having become man through the Virgin, he was tempted in all things according to the likeness of human nature yet did not experience sin. "He committed no sin, neither was any guile found in his mouth" (1Pt 2.22).
- Gregory of Nyssa, On Perfection
This is a restatement and emphasis on the Scriptural teaching that Christ was and is sinless.
If we have become brothers of the Lord who became the First-Born among many brothers through a similar rebirth by water and the Spirit, certain characteristics in our lives should manifest a close relationship to him, the First-Born of creation, who was conformed to our life. What characteristics of that form has scripture taught us? We have often said that "He committed no sin, nor was deceit found in his mouth" (1Pt 2.22). If we are to be named brothers of him who brought us into birth, innocence of life will constitute our relationship with him provided that no impurity separates us from a union in innocence.
- Gregory of Nyssa, On Perfection
This is yet another quotation of the Scriptural doctrine that Christ was sinless.
However, the mediator of God and man (1Tim 2.5) who joined the human race to God through his own person brings into union with God only that person who is worthy of it. When Christ united man to himself by the power of his divinity, he assumed part of our common nature not subject to nature's passions which excite us to sin (for it says "He committed no sin, nor was deceit found in his mouth"). Christ will unite each person with his divinity provided that they have no hindrance preventing their union with God.
- Gregory of Nyssa, On Perfection
This is another restatement and emphasis on the Scriptural teaching that Christ was and is sinless.
Only the Lord is free from the adversary's possessions; he conformed himself to us and our passions yet had no sin [Heb 4.15]. "The prince of this world is coming and he has no power over me" [Jn 14.30]. Anyone who takes care to cleanse himself by repentance can observe persons who allow virtue to shine through. Paul despised the evil of unbelief by accepting the gift of prophecy [Gal 2.8-9] since it had the treasure he sought. Isaiah lost all impurity of word and thought through purification by the divine coal [Is 6.6-7] and was filled by the Holy Spirit. He lost every bit by participating in the good or anything he reckoned contrary to it. And so, the temperate man loses licentiousness, the righteous loses unrighteousness, the modest person loses arrogance, the benevolent loses jealousy and the loving person loses hostility. Similarly, the blind man in the Gospel found what he did not have and lost what he already had [Mk 8.22-26], that is, the splendor of light took the place of his blindness. Also the leper received the boon of health [Mt 8.1-4], and life was bestowed upon those who rose from the dead while death passed away [Mk 1.40-45]. Therefore our teaching claims that we cannot possess anything on high unless we lose our earthly, humble qualities.
- Gregory of Nyssa, Commentary on Ecclesiastes, Seventh Homily
This final quotation puts the nail in the coffin. If we did not have this quotation, we would have only indirect affirmations of the unique sinlessness of Christ, but this quotation makes it explicit: "Only the Lord."
What about Mary? Did Gregory of Nyssa view her as sinless and somehow absentmindedly forget about her above? There is nothing in his teachings to suggest that. He does use the adjective "immaculate" of her, but only (as was traditionally the case) with respect to her body: she was an immaculate virgin, not simply a technical virgin or something like that.
Let us attempt to clarify our position and offer our own view. Human nature subsists by union of the intellectual soul with the body. However, both have their existence from a certain material substance. Man's material existence has its origin in the divine power; if anyone supposes his existence does not spring from this creative power, matter is sterile and does not come to life through [God's] creative activity. Just as this creative power brings man into existence by a union of body and soul, so does the power of the Most High exercise itself with regard to the Virgin's immaculate body in an immaterial fashion through the Spirit's vivifying where incorruptibility assumes matter in the virgin's body to create a fetus. And so, the New Man is formed who first and alone received this means of existence. He was formed according to God, not man, since the divine power equally pervaded his entire constitution. As a result, both parts of his constitution partook of divinity with a harmonious composition of soul and body.
- Gregory of Nyssa, Against Apollinarius
Notice that it is the virgin's immaculate body. The immaculateness of her body relates to the fact that no man had lain with her before the conception. Thus, Christ's conception was the opposite, in a sense, of our own glorification:
1 Corinthians 15:53-54
53 For this corruptible must put on incorruption, and this mortal must put on immortality. 54 So when this corruptible shall have put on incorruption, and this mortal shall have put on immortality, then shall be brought to pass the saying that is written, Death is swallowed up in victory.
Furthermore, from the same passage of Gregory, we can see that he viewed Christ's immaculate conception to be unique: "the New Man is formed who first and alone received this means of existence." Now, of course, that is primarily referring to having God as a father instead of a human father, but the whole event is unique and unparalleled.
I believe that [Christ] is both man and God, a statement complying with faith's correct interpretation and not with [Apollinarius'] inscription. For neither is the divinity earthly nor is humanity divine as he maintains; rather, the power of the Most High comes from above through the Holy Spirit [Lk 1.35] which overshadowed our human nature, that is, this power took on form, the spotless Virgin nourished it in human flesh, and he who was born from her was named Son of the Most High. The divine power which has its origin with the Most High thus assumed fellowship with mankind.
- Gregory of Nyssa, Against Apollinarius
Again, notice that the "spotless" aspect of the Virgin is in regard to her flesh. She was a spotless Virgin, not having even marred her virginity by intercourse with Joseph during Jesus' pregnancy.
This, I think, was the reason why our Master, Jesus Christ Himself, the Fountain of all innocence, did not come into the world by wedlock. It was, to divulge by the manner of His Incarnation this great secret; that purity is the only complete indication of the presence of God and of His coming, and that no one can in reality secure this for himself, unless he has altogether estranged himself from the passions of the flesh. What happened in the stainless Mary when the fullness of the Godhead which was in Christ shone out through her, that happens in every soul that leads by rule the virgin life.
- Gregory of Nyssa, On Virginity, Chapter 2
Likewise here, the "stainless" aspect of Mary is her virginity. Of course, there is some ambiguity. If someone wanted to try to impose a view of Mary being sinless, this is doubtless where they would attempt to do so, since there is some parallel between Mary and "every soul." But, in context, it is referring to the fact that Mary was "estranged ... from the passions of the flesh," meaning that she did not know Joseph before Jesus was born.
I searched in vain for additional references to Mary being "immaculate" in any sense in Gregory's writings. No further references were forthcoming. Nevertheless, some additional uses of that term (or terms like it) were to be found in Gregory's writings:
Such is the God of heresy. But what we, who, in the words of the Apostle, have been called to liberty by Christ, Who has freed us from bondage, have been taught by the Scriptures to think, I will set forth in few words. I take my start from the inspired teaching, and boldly declare that the Divine Word does not wish even us to be slaves, our nature having now been changed for the better, and that He Who has taken all that was ours, on the terms of giving to us in return what is His, even as He took disease, death, curse, and sin, so took our slavery also, not in such a way as Himself to have what He took, but so as to purge our nature of such evils, our defects being swallowed up and done away with in His stainless nature.
- Gregory of Nyssa, Against Eunomius, Book X, Chapter 4
The nature of Christ is stainless according to Gregory - no similar comment is ever made (that we can find) by Gregory of Mary.
For our Lord has announced that the life after our resurrection shall be as that of the angels. Now the peculiarity of the angelic nature is that they are strangers to marriage; therefore the blessing of this promise has been already received by him who has not only mingled his own glory with the halo of the Saints, but also by the stainlessness of his life has so imitated the purity of these incorporeal beings.
- Gregory of Nyssa, On Virginity, Chapter 13
In this example, the "stainlessness" that Gregory seems to have in mind is Christ's own virginity, although it could perhaps refer to Christ's sinlessness.
Indeed it has been revealed in the oracles of God, on what occasion to conceive and to bring forth is a good thing, and what species of fecundity was desired by God's saints; for both the Prophet Isaiah and the divine Apostle have made this clear and certain. The one cries, "From fear of You, O Lord, have I conceived;" the other boasts that he is the parent of the largest family of any, bringing to the birth whole cities and nations; not the Corinthians and Galatians only whom by his travailings he moulded for the Lord, but all in the wide circuit from Jerusalem to Illyricum; his children filled the world, "begotten" by him in Christ through the Gospel. In the same strain the womb of the Holy Virgin, which ministered to an Immaculate Birth, is pronounced blessed in the Gospel; for that birth did not annul the Virginity, nor did the Virginity impede so great a birth.
- Gregory of Nyssa, On Virginity, Chapter 19
Here we find further confirmation of the same principle. This is the only "immaculate birth" of which Gregory is aware (the only one that appears in his writings that we can find). It is the immaculate birth of Christ. Now, to be sure, there is some doctrine in Gregory's comments here that sounds more like a Gnostic or Roman Catholic view (especially the idea that "birth did not annul the Virginity, nor did the Virginity impede so great a birth"). But we can just accept the fact that Gregory was neither a Roman Catholic nor a Reformed Presbyterian. Like any Christian, his teachings were imperfect, but we must take him as he was, not try to change him into something he was not as our Romanist adversaries sometimes try.