linguistic:paraphrasing
Gregory at Constantinople

Upon the death of Emperor Valens in 378, the accession of Theodosius I, a steadfast supporter of Nicene orthodoxy, was good news to those who wished to purge Constantinople of Arian and Apollinarian domination. The exiled Nicene party gradually returned to the city. From his deathbed, Basil reminded them of Gregory's capabilities and likely recommended his friend to champion the Trinitarian cause in Constantinople.

In 379, the Antioch synod and its archbishop, Meletios, asked Gregory to go to Constantinople to lead a theological campaign to win over that city to Nicene orthodoxy. After much hesitation, Gregory agreed. His cousin Theodosia offered him a villa for his residence; Gregory immediately transformed much of it into a church, naming it Anastasia, "a scene for the resurrection of the faith". From this little chapel he delivered five powerful discourses on Nicene doctrine, explaining the nature of the Trinity and the unity of the Godhead. Refuting the Eunomion denial of the Holy Spirit's divinity, Gregory offered this argument:

Look at these facts: Christ is born, the Holy Spirit is His Forerunner. Christ is baptized, the Spirit bears witness to this... Christ works miracles, the Spirit accompanies them. Christ ascends, the Spirit takes His place. What great things are there in the idea of God which are not in His power? What titles appertaining to God do not apply also to Him, except for Unbegotten and Begotten? I tremble when I think of such an abundance of titles, and how many Names they blaspheme, those who revolt against the Spirit!

Gregory's homilies were well received and attracted ever-growing crowds to Anastasia. Fearing his popularity, his opponents decided to strike. On the vigil of Easter in 379, an Arian mob burst into his church during worship services, wounding Gregory and killing another bishop. Escaping the mob, Gregory next found himself betrayed by his erstwhile friend, the philosopher Maximus the Cynic. Maximus, who was in secret alliance with Peter, bishop of Alexandria, attempted to seize Gregory's position and have himself ordained bishop of Constantinople. Shocked, Gregory decided to resign his office, but the faction faithful to him induced him to stay and ejected Maximus. This episode left Gregory embarrassed, and exposed him to criticism as a provincial simpleton unable to cope with the intrigues of the imperial city.

Affairs in Constantinople remained confused as Gregory's position was still unofficial, and Arian priests yet occupied many important churches. The arrival of the emperor Theodosius in 380 settled matters in Gregory's favor. The emperor, determined to eliminate Arianism, expelled Bishop Demophilus. Gregory was subsequently enthroned as bishop of Constantinople at the Basilica of the Apostles, replacing Demophilus.