The Arian controversy was chiefly waged over the question of the eternal generation of the Son. By the time that Hilary began to write, every text of Scripture which could be made applicable to the point in dispute had been used to the utmost. There was little or nothing that remained to be done in the discovery or combination of passages. Of that controversy Athanasius was the hero; the arguments which he used and those which he refuted are admirably set forth in the introduction to the translation of his writings in this series. In writing the De Trinitate, so far as it dealt directly with the original controversy, it was neither possible nor desirable that Hilary should leave the beaten path. His object was to provide his readers with a compendious statement of ascertained truth for their own guidance, and with an armoury of weapons which had been tried and found effective in the conflicts of the day. It would, therefore, be superfluous to give in this place a detailed account of his reasonings concerning the generation of the Son, nor would such an account be of any assistance to those who have his writings in their hands. Hilary’s treatment of the Scriptural evidence is very complete, as was, indeed, necessary in a work which was intended as a handbook for practical use. The Father alone is unbegotten; the Son is truly the Son, neither created nor adopted. The Son is the Creator of the worlds, the Wisdom of God, Who alone knows the Father, Who manifested God to man in the various Theophanies of the Old Testament. His birth is without parallel, inasmuch as other births imply a previous non-existence, while that of the Son is from eternity. For the generation on the part of the Father and the birth on the part of the Son are not connected as by a temporal sequence of cause and effect, but exactly coincide in a timeless eternity Trin. xii. 21, ‘the birth is in the generation and the generation in the birth.’. Hilary repudiates the possibility of illustrating this divine birth by sensible analogies; it is beyond our understanding as it is beyond time. Nor can we wonder at this, seeing that our own birth is to us an insoluble mystery. The eternal birth of the Son is the expression of the eternal nature of God. It is the nature of the One that He should be Father, of the Other that He should be Son; this nature is co-eternal with Themselves, and therefore the One is co-eternal with the Other. Hence Athanasius had drawn the conclusion that the Son is ‘by nature and not by will’ Discourses against the Arians, iii. 58 ff; see Robertson’s notes in the Athanasius volume of this series, p. 426.; not that the will of God is contrary to His nature, but that (if the words may be used) there was no scope for its exercise in the generation of the Son, which came to pass as a direct consequence of the Divine nature. Such language was a natural protest against an Arian abuse; but it was a departure from earlier precedent and was not accepted by that Cappadocian school, more true to Alexandrian tradition than Athanasius himself, with which Hilary was in closest sympathy. In their eyes the generation of the Son must be an act of God’s will, if the freedom of Omnipotence, for which they were jealous, was to be respected; and Hilary shared their scruples. Not only in the De Synodis but in the De Trinitate E.g. Syn. 35, 37, 59, Trin. iii. 4, vi. 21, viii. 54.he assigns the birth of the Son to the omnipotence, the counsel and will of God acting in co-operation with His nature. This two-fold cause of birth is peculiar to the Son; all other beings owe their existence simply to the power and will, not to the nature of God Cf. Baltzer, Theologie d. hl. Hil. p. 19 f.. Such being the relation between Father and Son, it is obvious that They cannot differ in nature. The word ‘birth,’ by which the relation is described, indicates the transmission of nature from parent to offspring; and this word is, like ‘Father’ and ‘Son,’ an essential part of the revelation. The same divine nature or substance exists eternally and in equal perfection in Both, un-begotten in the Father, begotten in the Son. In fact, the expression, ‘Only-begotten God’ may be called Hilary’s watchword, with such ‘peculiar abundance Hort, Two Dissertations, p. 21, and cf. p. xvi., above.’ does it occur in his writings, as in those of his Cappadocian friends. But, though the Son is the Image of the Father, Hilary in his maturer thought, when free from the influence of his Asiatic allies, is careful to avoid using the inadequate and perilous term ‘likeness’ to describe the relation It constantly appears, though with all due safeguards, in the De Synodis, where sympathy as well as policy impelled him to approximate the language used by his friends. Similarly in Trin. iii. 23, he argues, from the admitted likeness, that there can be no difference. But, as we saw, this part of the De Trinitate is probably an early work, and does not represent Hilary’s later thought.. Such being the birth, and such the unity of nature, the Son must be very God. This is proved by all the usual passages of the Old Testament, from the Creation, onwards. These are used, as by the other Fathers, to prove that the Son has not the name only, but the reality, of Godhead; the reality corresponding to the nature. All things were made through Him out of nothing; therefore He is Almighty as the Father is Almighty. If man is made in the image of Both, if one Spirit belongs to Both, there can be no difference of nature between the Two. But They are not Two as possessing one nature, like human father and son, while living separate lives. God is One, with a Divinity undivided and indivisible Trin. v. 38.; and Hilary is never weary of denying the Arian charge that his creed involved the worship of two Gods. No analogies from created things can explain this unity. Tree and branch, fire and heat, source and stream can only illustrate Their inseparable co-existence; such comparisons, if pressed, lead inevitably to error. The true unity of Father and Son is deeper than this; deeper also than any unity, however perfect, of will with will. For it is an eternal mutual indwelling, Each perfectly corresponding with and comprehending and containing the Other, and Himself in the Other; and this not after the manner of earthly commingling of substances or exchange of properties. The only true comparison that can be made is with the union between Christ, in virtue of His humanity, and the believer Trin. viii. 13 ff.; such is the union, in virtue of the Godhead, between Father and Son. And this unity extends inevitably to will and action, since the Father is acting in all that the Son does, the Son is acting in all that the Father does; ‘he that hath seen Me hath seen the Father.’ This doctrine reconciles all our Lord’s statements in the Gospel of St. John concerning His own and His Father’s work.