I. The Orations. -- These -- forty-five in number -- raise him to equality with the best Orators of antiquity.
a. The Five Theological Orations. -- These won him the title of The Theologian. They were delivered in Constantinople, in defence of the Church's faith in the Trinity, against Eunomians and Macedonians. In the First and Second he treats of the existence, nature, being, and attributes of God, so far as man's finite intellect can comprehend them. In the Third and Fourth the subject is the Godhead of the Son, which he establishes by exposition of Scripture, and by refutation of the specious arguments brought forward by the heretics. In the Fifth he similarly maintains the Deity, and Personality of the Holy Ghost.
b. The Two Invectives against Julian. -- These were delivered at Nazianzus after the death of the Emperor, and present us with a very dark picture of his character. The orator dwells upon his attempt to rebuild the Temple at Jerusalem, and its failure, and his overthrow in the campaign against Persia. From these facts he demonstrates the power of God's Justice, and sets forth the Christian doctrine of the Divine Providence inculcating a lesson of trust in God.
c. Moral Orations. -- (1) The Apology for his flight. As was said above, it is most probable that this discourse was never actually spoken; if it was, it certainly must have been considerably enlarged afterwards. In it Gregory dwells on the motive of his flight and his return after his forced ordination; he speaks of his love of retirement, but most of all lays stress upon the difficulty of the Priestly Office, its heavy responsibilities and grave dangers, and upon his own sense of unworthiness. His return, he says, was prompted by respect for his hearers and by care for his aged parents; by the fear of losing his father's blessing; and by the recollection of what befel the Prophet Jonas on account of his resistance to the will of God. The remainder of the Oration is practically a treatise on the Priesthood, and was made use of by S. Chrysostom and S. Gregory the Great in their books on the subject.
(2) The Farewell Oration at Constantinople, containing an account of his work there.
(3) On Love of the Poor.
(4) On the Indissolubility of Marriage, the only Sermon of S. Gregory on a definite text which has come down to us.
(5) Three Orations on Peace.
(6) One on Moderation in theological discussion.
d. The Festal Orations. -- On Christmas, Epiphany (on the Baptism of Christ in the river Jordan, followed up next day by a long one on Holy Baptism), two on Easter (one of these his first sermon, the other almost if not quite his last). On Low Sunday, and on Pentecost.
e. Panegyrics on Saints. -- The Maccabee Brothers and their Mother; S. Cyprian of Carthage (in which there is evidence of the cultus of the Blessed Virgin Mary and of the practice of invocation of the Saints); and on S. Athanasius.
f. Funeral Orations on Eminent People. -- On his Father, preached before his Mother and S. Basil. On Cæsarius, in presence of his parents, consoling them by the picture of his brother's virtue, especially in having withstood Julian's efforts to pervert him, and in resigning his post at Court and leaving the Capital. On Gorgonia, whom he praises as a model Christian Matron, and whose wonderful cure before the Altar he relates. On S. Basil.
g. Occasional Orations, of which we mention three: (1) On a plague of hail. (2) On the consecration of Eulalius of Doara. (3) On his own consecration to Sasima.
II. The Letters, of which two hundred and forty-three are extant, are characterised by a clear, concise, and pleasant style and spirit. Some of them treat of the theological questions of the day, as for example the two to Cledonius, and one to Nectarius his Successor in the See of Constantinople; these deal with the Apollinarian errors. Most of them however are letters to private friends; sometimes of condolence or congratulation, sometimes of recommendation, sometimes on mere general subjects of interest. To this section must be ascribed his Will, which is probably genuine.
III. The Poems, five hundred and seven in number, are in various metres. While leaving much to be desired, these verses shew much real poetic feeling, and at times rise to genuine beauty. Thirty-eight are dogmatic, on the Trinity, on the works of God in Creation, on Providence, on Angels and Men, on the Fall, on the Decalogue, on the Prophets Elias and Elissæus, on the Incarnation, the Miracles and Parables of our Lord, and the canonical Books of the Bible. Forty are Moral; two hundred and six Historical and Autobiographical; one hundred and twenty-nine are Epitaphs, or rather funeral Epigrams; ninety-four are Epigrams.
There is also a long Tragedy, called Christus Patiens which is the first known attempt at a Christian drama; the parts are sustained by Christ, The Blessed Virgin, S. Joseph, S. Mary Magdalene, Nicodemus, Pontius Pilate, Theologus, Nuntius, and others. The Benedictine Editors however doubt the genuineness of this Tragedy and Caillau, who published the second volume of this Edition after the troubles of the French Revolution, thinks it is to be ascribed to another Gregory, Bishop of Antioch in the Sixth Century, and relegates it to an Appendix. None of The Theologian's Odes or Hymns have, however, found a place in the liturgical poetry of the Church.