translation....Critics have rivalled each other in the praises they have heaped upon them, but no praise is so high as that of the many Theologians who have found in them their own best thoughts. A Critic who cannot be accused of partiality towards Gregory has given in a few words perhaps the truest estimate of them: A solidity of thought, the concentration of all that is spread through the writings of Hilary, Basil, and Athanasius, a flow of softened eloquence which does not halt or lose itself for a moment, an argument nervous without dryness on the one hand, and without useless ornament on the other, give these five Discourses a place to themselves among the monuments of this fine Genius, who was not always in the same degree free from grandiloquence and affectation. In a few pages, and in a few hours, Gregory has summed up and closed the controversy of a whole Century.'"  They were preached in the Church called Anastasia,  at Constantinople, between 379 and 381, and have gained for their author the title of The Theologian, which he shares with S. John the Evangelist alone. It should perhaps, however, be noted that the word is not here used in the wide and general sense in which we employ it, but in a narrower and more specific way, denoting emphatically the Defender of the Deity of the Logos. His principal opponents were the followers of Eunomius and Macedonius, and it is almost entirely against them that these Orations on Theology, or the Godhead of the Word and the Holy Ghost, are directed. The chief object of the Preacher in these and most other of his public utterances, is to maintain the Nicene Faith of the Trinity or Trinity of God; that is, the Doctrine that while there is but One Substance or Essence  in the Godhead, and by consequence God is in the most absolute sense One, yet God is not Unipersonal, but within this Undivided Unity there are three Self-determining Subjects or Persons, distinguished from one another by special characteristics (idiotetes) or personal properties -- Father, Son, and Holy Ghost. With this object he entered into conflict with the heretics named above, who denied either the Consubstantiality of the Son with the Father, or the perfect Godhead and Personality of the Holy Ghost.
Eunomius, whom Ullmann calls one of the most interesting heretics of the Fourth Century, was by birth a Cappadocian, and slightly older than Gregory. As a young man he was a pupil and amanuensis of Aëtius, by whom the Arian heresy was developed to its extreme results. The disciple never shrank from drawing the furthest logical conclusions from his master's premises, or from stating them with a frankness, which to those who regarded the premises themselves from which he reasoned as horrible blasphemies, seemed nothing less than diabolical in its impiety. So precisely did he complete and formulate his teacher's heretical tenets, that the Anomoean Arians were ever afterwards called Eunomians, rather than Aëtians. They asserted the absolute Unlikeness of the Being of the Father and of the Son. Starting with the conception of God as Absolute Being, of Whom no Generation can be predicated, Unbegotten and incapable of Begetting, they went on to say that an Eternal Generation is inconceivable, and that the Generation of the Son of God must have had a beginning. Of course, therefore, the Arian conclusion followed, namely, that there was a time when the Son did not exist (en pote hote ouk en), and His Essence is altogether unlike that of the Unbegotten Father. Equality of essence and Similarity of essence, are alike untenable, from the mere fact that the one Essence is Unbegotten, and the other is Begotten. The Son, they said, is the First Creation of the Divine Energy, and is the Instrument by whom God created the world, and in this sense, as the Organ of creative power, may be said to be the Express Image and Likeness of the Energy of the Father. 
As they viewed the Holy Ghost as sharing the Divine Nature in an even remoter degree, as being only the noblest production of the Only-begotten Son, Eunomius was the first person heretically to discontinue the practice of threefold immersion in Holy Baptism. He also corrupted the Form of that Sacrament, by setting aside the use of the Name of the Father, Son, and Holy Ghost, and baptizing people "in the name of the Creator, and into the death of Christ." Therefore the Council of Constantinople ordered that converts from Eunomianism should be baptized, although those from other forms of Arianism were admitted into the Catholic Church by simple imposition of hands. Through the influence of the followers of Aëtius, Eunomius became, in 360, Bishop of Cyzicus in Mysia, but he does not appear to have occupied the See very long. At any rate when Gregory came, in 379, to Constantinople, he was living in retirement near Chalcedon. All parties concur in representing him as a consummate Dialectician, but the Orthodox declared that he had turned Theology into a mere Technology. Readiness of Dialectic was the great characteristic of his Sect, and it was they who introduced into the Capital that bad spirit of theological disputatiousness which Gregory deplores in the first of these famous Orations. He also differed entirely from Gregory, not merely in the conclusions at which he arrived, but in the method by which he reached them; following the system of Aristotle, rather than of Plato, and using an exclusively intellectual method, while Gregory treated Religion as belonging to the entire man. The point at issue between them, besides this of the Interior relations of the Three Blessed Persons within the Godhead, was mainly the question as to the complete comprehensibility of the Divine Nature, which the Eunomians maintained, and Gregory denied. The latter argued that, while we have a sure conviction that God is, we have not a full understanding of What He is. He would not, however, exclude us from all knowledge of God's Nature, only he limits our capacity to so much as God has been pleased to reveal to us of Himself. "In my opinion," he says (Or. xxiv.4), "it is impossible to express God, and yet more impossible to conceive Him -- seeing that the thick covering of the flesh is an obstacle to the understanding of the truth." Similarly in the Fourth of these Orations (Or. xxx.17) he says, "The Deity cannot be expressed in words. And this is proved to us, not only by arguments, but by the wisest and most ancient of the Hebrews, so far as they have given us reason for conjecture. For they appropriated certain characters to the honour of the Deity, and would not even allow the name of anything inferior to God to be written with the same letters as that of God, because to their mind it was improper that the Deity should even to that extent admit any of His creatures to a share with Himself. How then could they have admitted that the indivisible and separate Nature can be explained by divisible words?"
In the mind of Gregory, the Orthodox doctrine of the Blessed Trinity is the fundamental dogma of Christianity, in contrast with all other religions, and with all heretical systems. "Remember your confession," he says to his hearers in an Oration against the Arians; "Into what were you baptized? The Father? Good, but still Jewish. The Son? Good; no longer Jewish, but not yet perfect. The Holy Ghost? Very good; this is perfect. Was it then simply into these, or was there some one common Name of these? Yes, there was, and it is God." And in the same oration he calls Arianism a new Judaism, because it ascribes full Deity only to the Father; and he speaks of One Nature in Three Individualities, intelligent, perfect, self-existent, distinct numerically, but one in Godhead. "In created things," says Ullmann, "the several individuals are embraced in a common conception, though in themselves only connected together in thought, while in fact they are not one. Manhood is only an intellectual conception; in fact there exist only Men. But in the Godhead the Three Persons are not only in conception, but in fact, One; and this Unity is not only a relative but an absolute Unity, because the Divine Being is perfect in all Three Persons, and in all in a perfect equality. In this sense therefore Gregory and all orthodox Trinitarians maintain the Unity of God. But within this Unity there is a true Trinity, Father, Son, and Holy Ghost, a Trinity of Persons in a Unity of Nature." We worship, he says (Or. xxxiii.16), the Father, Son, and Holy Ghost, One Nature in Three Individualities. So that, as he says elsewhere (Or. in laud. Athanasii, xxi.10), the Trinity is a true Trinity; not a numbering of unlike things, but a binding together of equals. Each of the Persons is God in the fullest sense. The Son and the Holy Ghost have their Source of Being in the Father, but in such sense that They are fully consubstantial with Him, and that neither of Them differs from Him in any particular of Essence. The points of difference lie in the Personal Attributes; the Father Unoriginate, and Source of Deity; the Son deriving His Being eternally from the Father, and Himself the Source of all created existence; the Holy Ghost proceeding eternally from God, and sent into the world.
In the first of these five discourses the Preacher sets himself to clear the ground for the fitting presentation of his great theme. He endeavours to lay down the principles on which Theologians should proceed in such discussions, and very earnestly deprecates the habit of promiscuous argument in all sorts of places, upon all sorts of occasions, and before all sorts of hearers, of the deepest and most sacred truths and mysteries of the Faith. They only should be allowed to engage in such conversation who are fitted for it by the practice of Christian virtue. For others there are many other subjects upon which they can exercise their dialectical attainments, without doing or incurring any injury.
In the second oration Gregory lays down the position referred to above, that it is impossible for even the most exalted human reason fully to grasp the Nature of God, though His Existence is patent to all. We can only, he says, predicate negatives concerning Him. He gives three reasons for this incapacity. First to enhance our estimation of this knowledge, when attained hereafter; secondly to save us from the danger of falling through pride, like Lucifer, if we attained it prematurely; and thirdly, to support and sustain us in the trials and conflicts of this life, by the certainty that its attainment hereafter will be the reward of faithful service in them. The cause of our present inability is the body with which our soul is united, the grossness of whose present condition hinders us from rising to the complete apprehension of the invisible and immaterial. God, out of compassion for our weakness, has been pleased to designate Himself in Holy Scripture by various names taken from material objects, or from moral virtues; but these are only stepping-stones to the truth, and have indeed been sometimes perverted, and made a basis for polytheism. It is, however, only natural that the Divine Essence should be shrouded in Mystery, for the same is the case with the created essences also.
In the Third and Fourth he deals with the question of the Son. His position may be summed up as follows: The Son is absolutely of One Substance with the Father, and shares with Him all the Attributes of Godhead. Yet He is a distinct Person, marked off by the fact that He is begotten of the Father. But we must be careful not to allow this term "Begotten" to suggest to us any analogy with created things. It is wholly independent of time and space and sense.
This position he had to defend against many assailants, and especially against the Eunomians. These heretics maintained that the use of this term necessarily implied a beginning of the Essence of the Son, and they asked the orthodox to tell them when that beginning took place. Gregory replies that the Generation of God the Son is beyond all time; pointing out that Paternity is an Essential attribute of God the Father, and therefore is as eternal as His Essence, so that there never was a time when He was not the Father, and consequently never a time when the Generation of the Son began. He admits that there is a sense in which it is possible to say that the Son and the Spirit are not unoriginate, but then you must be careful not to use the word Origin in the sense of Beginning, but in that of Cause. They derive Their Being eternally from the Father, and all Three Persons are coeternal together. In respect of cause They are not unoriginate, but the cause is not necessarily prior in time to its effect, just as the Sun is not prior to its own light. In respect of time, then, They may be said to be unoriginate, for the Sources of time cannot be subject to time. "If the Father has not ceased to beget, His Generation is an imperfect one; and if He has ceased, He must have begun, for an end implies a beginning." "Not so," says Gregory, "unless you are prepared to admit that what has no end has necessarily no beginning; and in that case what will you say about the Angels, or the human soul? These will have no end; had either of them therefore no beginning?" By a similar process of Reductio ad absurdum he dissipates all the quibbles of Eunomian sophistry, and lays down the orthodox Faith of the Church. Then in the remainder of the Third and Fourth Orations he goes on to examine the Scriptural testimony adduced by his opponents, and to shew by a similar catena on the other side that the overwhelming preponderance of the authority of the Bible is clearly against them. In connection with this point he lays down the canon that in the interpretation of Scripture in regard to our Lord, all expressions savouring of humility or weakness are to be referred to that pure Humanity which He assumed for our sake; while all that speaks of Majesty and Power belongs to His Godhead.
In the Fifth he deals with the doctrine of the Holy Ghost. The heresy of Arius was at first directly concerned only with the Person of our Lord, though not without a side-glance at that also of the Holy Ghost. The Council of Nicæa had confined itself to the first question, and its Creed ended with, "We believe in the Holy Ghost." This, it was afterwards argued, was enough to proclaim His Divinity, and so Gregory argues in this Oration, "If He be only a creature, how do we believe on Him, how are we made perfect in Him, for the first of these belongs to Deity, the second may be said of anything" (c. vi.). The reason, however, that the Great Synod made no express definition on the point seems to have been that the controversy had not yet been carried so far in direct terms (cf. S. Basil, Epp. lxxviii. ccclxxxvii.). But fifty years later the growth of the heresy rendered a definition of the Church's faith on this point needful; and in 363, on his return from his fourth period of exile, S. Athanasius held a provincial Synod at Alexandria, in whose Synodical Letter to the Emperor Jovian the Godhead of the Holy Ghost is maintained in terms which, as Canon Bright says, partly anticipate the language of the Creed of Constantinople (Dict. Biog. Art. Athanasius). The new development of the heresy had begun to appear at Constantinople as well as in Thrace and Asia Minor. Macedonius, a Semi-Arian, had been elected Bishop of Constantinople in 341, and in spite of violent opposition, which he met by still more violent measures, had maintained his position till 360, when he was deposed and driven out by the Anomoean Arians. He then in his retirement became the leader of the Semi-Arian party. Accepting the statement that the Son was Like in Essence to the Father, he would not concede even this to the Holy Ghost, but declared Him to be a mere creature (Thdt. Hist. Eccl. ii.6), and the servant or minister of the Son; applying to Him terms which without error could only be used of the Angels (Sozomen. H. E. iv.27). His followers were known as Macedonians, or sometimes Marathonians, from a certain Marathonius, formerly a Paymaster of the Prætorian Guards, who had become a Deacon of Constantinople, and, having done much in the way of founding and maintaining Monastic Houses and Houses of Charity in the City, was consecrated by Macedonius as Bishop of Nicomedia. They were also known as Pneumatomachi, from the nature of their Heresy. A controversy had now begun to arise as to the precise position which the true faith was to assign to the Holy Spirit. There were those who left it doubtful whether He had indeed a separate Personality, or whether He were not rather a mere Influence or Activity of the Father and the Son. Gregory tells us how, when he came to the Metropolis, he found the wildest confusion prevalent. Some, he says, conceived of the Holy Ghost as a mere Energy of God, others thought Him a Creature, others believed Him to be God; while many out of an alleged reverence for Holy Scripture, hesitated to give Him the Name of God. To this last class belonged, according to Socrates (H. E. ii.45), Eustathius, who had been ejected from the Bishopric of Sebasteia in Pontus. He refused to admit that the Holy Spirit is God, while yet He did not dare to affirm that He is a mere creature. When Gregory proceeded to preach the Deity of the Spirit, he was accused of introducing a strange and unscriptural god, because, as he acknowledges, the letter of the Bible is not so clear on the doctrine of the Spirit as it is on that of the Son. But he points out that it is possible to be superstitious in one's reverence for the letter of the Bible, and that such superstition leads directly to heresy. He explains the reticence of the New Testament on this point by shewing (in this Oration, cc.26, 27) how God's Self-Revelation to man has always been a gradual one; how the Old Testament revealed the Father clearly, with obscure hints about the Son; and the New Testament manifested the Son, but only hinted at the Godhead of the Spirit; but now, he says, the Spirit dwells among us, and allows us to recognize Him more clearly. For it would not have been advisable, as long as the Godhead of the Father was not acknowledged, to proclaim that of the Son; and while the Deity of the Son was not yet accepted, to add another burden in that of the Holy Spirit. Recognizing thus a Divine economy in the Self-Revelations of God, he was not averse to using a similar caution in his own dealings with weak or ill-instructed minds.  But yet when real necessity arose, he could speak out with perfect plainness on this subject; and he even incurred danger to life and limb from the violence of the opposing party. He met their opposition by the clearest statements of the Catholic Dogma. "Is the Spirit God?" he asks. "Yes." "But is He consubstantial?" "Yes, if He is God." (Orat. xxxi.10.) He appeals both to the Bible, and to the experience of the Christian life. If the Spirit is not to be adored, how can He deify me in Baptism? From the Spirit comes our new Birth; from the new Birth our new Life; and from the new Life our knowledge of the Dignity of Him from Whom it is derived (Ibid. C.29). He is, however, milder in his treatment of these heretics than of the strict Arians, both, as he says, because they approached more nearly to the Orthodox belief on the subject of the Son, and because their conspicuous piety of life shewed that their error was not altogether wilful. In this Oration he shows that though the Name of God may not actually be given in the New Testament to the Holy Ghost, yet all the attributes of God are ascribed to Him, and that therefore the use of the Name is a matter of legitimate inference. He carries on the argument in the Oration on Pentecost (No. XLI. See the Introduction to that Oration in the present Volume).
With regard to the doctrine of the Procession, Gregory gives us no clear information. He is silent as to the Procession from the Son. It is enough for him that the Spirit is not Begotten but Proceeding (in SS. Lumina, c.12), and that Procession is His distinctive Property, which involves at once His Personality and His Essential Deity.
At length in 381 the work of local Synods and episcopal conferences was completed and clinched by the Ruling of a Second Ecumenical Council. It is true that the Council which Theodosius summoned to meet at Constantinople could scarcely have regarded itself as possessing Ecumenical authority; whilst in the West it certainly was not regarded in this light before the Sixth Century. Nevertheless the honours of Ecumenicity were ultimately awarded to it by the whole Church, because it completes the series of Great Councils by which the Doctrine of the Deity of the Holy Spirit was affirmed; and in fact it expressed the final judgment of the Catholic Church upon the Macedonian controversy. Its first Canon anathematises the Semiarians or Pneumatomachi by name as well as the Eunomians or Anomoean Arians (cf. Dict. Biog. Art. Gregory of Nazianzus, by Dr. H. B. Swete).
 De Broglie, "L'Eglise et l'Empire," v. 385.--"Ce sont autant de modèles dans l'art délicat d'imprimer la forme oratoire aux développements philosophiques. Une pensée substantielle, formée de tous les sucs répandus dans les écrits d'Hilaire, de Basile et d'Athanase; un courant d'éloquence tempérée qui ne se ralentit, ni ne s'égare en aucun moment; une argumentation nerveuse sans sècheresse, mais sans vaine parure d'ornements, font à ces cinq discours une place à part parmi les monuments de ce beau génie, auquel l'emphase et l'affectation ne furent pas toujours aussi étrangers. En quelques pages, et en quelques heures, Grégoire avait résumé et clos la controverse de tout un siècle."  See Prolegomena p. 171.  "There is but one divine Essence or Substance; Father, Son, and Spirit, are one in essence, or consubstantial. They are in one another, inseparable, and cannot be conceived without each other. In this point the Nicene doctrine is thoroughly monotheistic, or monarchian, in distinction from tritheism, which is but a new form of the polytheism of the pagans. "The terms Essence (ousia) and Nature (phusis), in the philosophical sense, denote not an individual, a personality, but the Genus or Species; not Unum in Numero, but Ens Unum in Multis. All men are of the same substance, partake of the same human nature; though as persons and individuals they are very different. The term Homo-ousion, in its strict grammatical sense, differs from Mono-ousion or Touto-ousion, as well as from Hetero-ousion, and signifies not numerical identity, but equality of essence or community of nature among several beings. It is clearly thus used in the Chalcedonian Symbol, where it is said that Christ is consubstantial (Homo-ousios) with the Father as touching the Godhead, and consubstantial with us (and yet individually distinct from us) as touching the Manhood.' But in the Divine Trinity consubstantiality denotes not only sameness of kind, but at the same time Numerical unity; not merely the Unum in Specie, but also the Unum in Numero. The three Persons are related to the Divine Substance not as three individuals to their species, as Abraham, Isaac, and Jacob, or Peter, John, and Paul, to human nature; they are only one God. The divine Substance is absolutely indivisible by reason of its simplicity, and absolutely inextensible and untransferable by reason of its infinity; whereas a corporeal substance can be divided, and the human nature can be multiplied by generation. Three Divine substances would limit and exclude each other, and therefore could not be infinite or absolute. The whole fulness of the one undivided Essence of God, with all its attributes, is in all the Persons of the Trinity, though in each in His own way; in the Father as Original Principle, in the Son by eternal Generation, in the Spirit by eternal Procession. The Church teaches not One Divine Essence and Three Persons, but One Essence In Three Persons. Father, Son, and Spirit cannot be conceived as Three separate individuals, but are in one another, and form a solidaric Unity." (Schaff, History of the Church, Nic. & Post-Nic. Period, Div. ii.[p. 672.)  Two terms borrowed from Holy Scripture (Hebrews 1:3). But observe, borrowed with a difference--not "the Image of His Substance," which they would not admit, but of His "Energy," which is a very different conception.  In his Fifty-third Epistle, addressed to S. Basil, there is an amusing instance of his defence of this tolerant disposition, which S. Basil also displayed in dealing with minds of this class.
 See Prolegomena p. 171.
 "There is but one divine Essence or Substance; Father, Son, and Spirit, are one in essence, or consubstantial. They are in one another, inseparable, and cannot be conceived without each other. In this point the Nicene doctrine is thoroughly monotheistic, or monarchian, in distinction from tritheism, which is but a new form of the polytheism of the pagans. "The terms Essence (ousia) and Nature (phusis), in the philosophical sense, denote not an individual, a personality, but the Genus or Species; not Unum in Numero, but Ens Unum in Multis. All men are of the same substance, partake of the same human nature; though as persons and individuals they are very different. The term Homo-ousion, in its strict grammatical sense, differs from Mono-ousion or Touto-ousion, as well as from Hetero-ousion, and signifies not numerical identity, but equality of essence or community of nature among several beings. It is clearly thus used in the Chalcedonian Symbol, where it is said that Christ is consubstantial (Homo-ousios) with the Father as touching the Godhead, and consubstantial with us (and yet individually distinct from us) as touching the Manhood.' But in the Divine Trinity consubstantiality denotes not only sameness of kind, but at the same time Numerical unity; not merely the Unum in Specie, but also the Unum in Numero. The three Persons are related to the Divine Substance not as three individuals to their species, as Abraham, Isaac, and Jacob, or Peter, John, and Paul, to human nature; they are only one God. The divine Substance is absolutely indivisible by reason of its simplicity, and absolutely inextensible and untransferable by reason of its infinity; whereas a corporeal substance can be divided, and the human nature can be multiplied by generation. Three Divine substances would limit and exclude each other, and therefore could not be infinite or absolute. The whole fulness of the one undivided Essence of God, with all its attributes, is in all the Persons of the Trinity, though in each in His own way; in the Father as Original Principle, in the Son by eternal Generation, in the Spirit by eternal Procession. The Church teaches not One Divine Essence and Three Persons, but One Essence In Three Persons. Father, Son, and Spirit cannot be conceived as Three separate individuals, but are in one another, and form a solidaric Unity." (Schaff, History of the Church, Nic. & Post-Nic. Period, Div. ii.[p. 672.)
 Two terms borrowed from Holy Scripture (Hebrews 1:3). But observe, borrowed with a difference--not "the Image of His Substance," which they would not admit, but of His "Energy," which is a very different conception.
 In his Fifty-third Epistle, addressed to S. Basil, there is an amusing instance of his defence of this tolerant disposition, which S. Basil also displayed in dealing with minds of this class.