Concerning [Christ] we thus believe, even as the Apostolic Church believes. In one Father unbegotten, who has from no one the cause of His being, who is unchangeable and immutable, who is always the same, and admits of no increase or diminution; who gave to us the Law, the prophets, and the Gospels; who is Lord of the patriarchs and apostles, and all the saints. And in one Lord Jesus Christ, the only-begotten Son of God; not begotten of things which are not, but of Him who is the Father;.... And besides the pious opinion concerning the Father and the Son, we confess to one Holy Spirit, as the divine Scriptures teach us; who hath inaugurated both the holy men of the Old Testament, and the divine teachers of that which is called the New. And besides, also, one only catholic and Apostolic Church, which can never be destroyed, though all the world should seek to make war with it; but it is victorious over every most impious revolt of the heretics who rise up against it. For her [head] has confirmed our minds by saying, "Be of good cheer, I have overcome the world." After this we know of the resurrection of the dead, the first-fruits of which was our Lord Jesus Christ, who in very deed, and not in appearance merely, carried a body, of Mary Mother of God, who in the end of the world came to the human race to put away sin, was crucified and died, and yet did He not thus perceive any detriment to His divinity, being raised from the dead, taken up into heaven, seated at the right hand of majesty.
These things in part have I written in this epistle, thinking it burdensome to write out each accurately, even as I said before, because they escape not your religious diligence. Thus do we teach, thus do we preach. These are the apostolic doctrines of the Church, for which also we die, esteeming those but little who would compel us to forswear them, even if they would force us by tortures, and not casting away our hope in them.

-- 'Epistle' to Alexander, Bishop of the City of Constantinople (12, 13)

Gregory was a real Renaissance man born about 600 years before the Renaissance. From a holy family he became a monk early and spent most of his life teaching theology in that monastery (a monastery which, incidentally, lasted until the Armenian Genocide of the 20th century). A prolific theologian and writer, he is well recognized in the East, especially the Armenian Apostolic Church. In the West he has an "equipollent canonization" (basically recognizing his canonization by the East in the West without all the rigamarole) and proclaimed a Doctor of the Universal Church on 12 April 2015 by Pope Francis, making him one of the newest Doctors in the Church.
The thing is, the Armenian Apostolic Church rejected the doctrines of the Council of Chalcedon. So how is that a Church that rejected Chalcedon ("confess Chalcedon or take a beatin'!") can produce a Doctor of the Universal Church?
The Council of Florence in 1439 contains a bull of reunion with these Armenians, and Pope Benedict XIV in the 1700's saw those bulls as having merit and effect, regardless of the ups and downs in the relationship. John Paul II produced a common declaration (recognizing their liturgy and liturgical calendar among other doctrinal issues and things) with the head of the Armenian Apostolic Church in the 1990's and in fact uses Gregory as an example in his encyclical Redemptoris Mater, and allowed a reference to him in The Catechism of the Catholic Church (§2678).
That "they may all be one, as you, Father, are in me and I in you" Christ prays. Let us pray it with him!
Extra shout out to Baldomerus of Saint Justus, a blacksmith recognized for his selfless love and holiness, who became a monk late in life at the Monastery of St. Justus.

Now what prayers in this book may be pleasing to you,
what acceptable smoke of incense shall I offer to you,
O Christ, praised heavenly King,
if I do not pray to you to bless those whom I cursed,
tend to those I have bruised,
care for those I have alienated,
give refuge to those I have betrayed,
And heal the souls of those I have wounded in body?

-- From his Book of Lamentation

Jesus spoke to the crowds and to his disciples, saying, “The scribes and the Pharisees have taken their seat on the chair of Moses. Therefore, do and observe all things whatsoever they tell you, but do not follow their example. For they preach but they do not practice. They tie up heavy burdens hard to carry and lay them on people’s shoulders, but they will not lift a finger to move them. All their works are performed to be seen. They widen their phylacteries and lengthen their tassels. They love places of honor at banquets, seats of honor in synagogues, greetings in marketplaces, and the salutation ‘Rabbi.’ As for you, do not be called ‘Rabbi.’ You have but one teacher, and you are all brothers. Call no one on earth your father; you have but one Father in heaven. Do not be called ‘Master’; you have but one master, the Christ. The greatest among you must be your servant. Whoever exalts himself will be humbled; but whoever humbles himself will be exalted.”

-- Matthew 23:1-12