About the year 379, St. Gregory came to the assistance of the Church of Constantinople, which had been troubled for forty years by the Arians; with his supremely wise words and many labors he freed it from the corruption of heresy. He was elected archbishop of that city by the Second Ecumenical Council. When St. Gregory came to Constantinople, the Arians had taken all the churches and he was forced to serve in a house chapel dedicated to St. Anastasia the Martyr. From there he began to preach his famous five sermons on the Trinity, called the Triadica. When he left Constantinople two years later, the Arians did not have one church left to them in the city. St. Meletius of Antioch, who was presiding over the Second Ecumenical Council, died and St. Gregory was chosen in his stead; there he distinguished himself in his expositions of dogmatic theology.

Having governed the Church until 382, he retired from the See of Constantinople, returned to Nazianzus, where he lived to the end of his life. He reposed in the Lord in 391, having lived some sixty-two years.

His extant writings, both prose and poems, demonstrate his lofty eloquence and his wondrous breath of learning. He is considered to have surpassed the Greek writers of antiquity, and because of his God-inspired theological thought, he received the surname “Theologian.” His feast day is January 25.   (from Othodoxwiki.org)