Short answers, pulled from the story.
Gregory of Nyssa was a 4th-century Christian theologian and bishop who served the see of Nyssa from 372 to 376 and again from 378 until his death in 394. He is significant as one of the Cappadocian Fathers, as an early proponent of Christian universalism, and as the first person in recorded history to write against all forms of slavery, declaring the institution inherently sinful.
Gregory argued that no being created by God would ultimately fall outside the Kingdom of God, drawing on Paul's declaration that God will be "all in all." He taught that some would be purified in this life, others healed through fire in the afterlife, and that eventually every person would be offered participation in God's blessings. Most scholars affirm that universal restoration, or apokatastasis, was genuinely what Gregory believed and taught.
Gregory of Nyssa wrote the first and only sustained critique of the institution of slavery itself made in the ancient world, arguing that no human being could rightfully own another because each person is made in the image of God. Philosophers such as Plato, Aristotle, and Seneca either supported slavery or merely urged humane treatment without questioning the institution. Scholars note that no comparable unequivocal stance against slavery appeared again until the nineteenth century abolitionist movement.
The Cappadocian Fathers are Gregory of Nyssa, his elder brother Basil of Caesarea, and their friend Gregory of Nazianzus. All three were fourth-century Christian theologians who made formative contributions to the doctrine of the Trinity and the Nicene Creed. They are collectively venerated as saints across Eastern Orthodoxy, Catholicism, Anglicanism, and Lutheranism.
Epektasis is Gregory of Nyssa's concept of the soul's endless progression toward God. Because God is infinite and created beings are finite, Gregory taught that no one can ever fully comprehend God; instead, the soul perpetually advances, transcending whatever level of understanding it has reached. In the Life of Moses, he describes three stages of this journey: an initial darkness of ignorance, spiritual illumination, and finally a deeper darkness in mystic contemplation of God.
Eastern Orthodox, Eastern Catholic, and Lutheran churches commemorate Gregory of Nyssa on the 10th of January. The Latin Church, in editions of the Roman Martyrology published after the year 2000, also lists his feast on the 10th of January, though earlier editions placed it on the 9th of March. The Church of England commemorates Gregory together with Macrina the Younger on the 19th of July.