Gregory of Nyssa (Greek: Άγιος Γρηγόριος Νύσσης; Latin: Gregorius Nyssenus; Arabic: غريغوريوس النيصي) (c 335 – after 394) was a Christian bishop and saint. He was a younger brother of Basil the Great and a good friend of Gregory Nazianzus. His significance has long been recognized in the Eastern Orthodox, Oriental Orthodox, and Roman Catholic branches of Christianity. Some historians identify Theosebia the deaconess as his wife, others hold that she, like Macrina the Younger, was also a sister of Gregory and Basil.
Gregory is the first Christian theologian to argue for the infinity of God and to contain a marked universalist tone. Origen of Alexandria, a major influence on Gregory, had explicitly argued that God is limited, an essential notion in Platonism, since to be limited is to be clearly defined and knowable. Gregory, however, argues that if God is limited he must be limited by something greater than himself. As there is nothing greater than God, He is therefore without boundaries, and thus infinite. The idea had already been developed by neoplatonic philosophers, especially Plotinus, another important influence on Gregory, but he is the first Christian to defend it, apart from some hints in the work of Irenaeus of Lyons.
Accordingly, Gregory argues that since God is infinite he cannot be comprehended. Origen had spoken of the spiritual journey as a progression of increasing illumination, as the mystic studies Scripture and comes to learn more about God. Nyssa taught on the other hand that God was knowable in his manifestations but that ultimately one must transcend knowledge or gnosis (since knowledge is based on reflection). Gnosis is limited and can become a barrier between man and God. If one wishes to commune with God one must enter into the Divine filial relation with God the Father through Jesus Christ, one in ousia with the Father which results in pure faith without any preconceived notions of God. Once one reaches this point one can commune with God just as Moses did in Nyssa's mystical classic, The Life of Moses.
Like earlier authors, including Philo, he uses the story of Moses as an allegory for the spiritual life. Moses first meets God in the burning bush, a theophany of light and illumination, but then he meets him again in the cloud, where he realises that God cannot be seen by the eyes. Ascending Mount Sinai, he finally comes to the "divine darkness", and realises that God cannot be known by the mind either.
It is only through not-knowing and not-seeing that God can, paradoxically, be known and seen, knowledge that can only be gained through an "ascending life of holiness." This notion would be extremely influential in both Western and Eastern spirituality, via the mystical writings of Pseudo-Dionysius the Areopagite, and later in the anonymous 14th century work, The Cloud of Unknowing. Thus he is a major figure in the history of apophatic theology and spirituality.
Related to this is Gregory's idea of epektasis or constant progress. The platonic philosophy was that stability is perfection and change is for the worse. In contrast, Gregory described the ideal of human perfection as constant progress in virtue and godliness. In his theology, God himself has always been perfect and has never changed, and never will. Humanity fell from grace in the Garden of Eden, but rather than return to an unchanging state, humanity's goal is to become more and more perfect, more like God, even though humanity will never understand, much less attain, God's transcendence. This idea has had a profound influence on the Eastern Orthodox teaching regarding theosis or "divinization".
Gregory thus shared Origen of Alexandria's conviction that man's material nature is a result of the fall and also Origen's hope for ultimate universal salvation. While the question of salvation or damnation is settled at the moment of death, nobody is known to have been damned and so prayers are offered for absolutely all the dead, even for those who seem to have been great sinners.
Systematic publication of his works is proceeding in a collection, Gregorii Nysseni Opera, dominated by the work of the philologist, Werner Jaeger.
Several volumes of his writings have appeared in the Sources Chrétiennes collection, the first publication of which was Daniélou's translation (later edition) of his Life of Moses (1941).