Book VII. The Arians are adepts at concealing their meaning; at the use of Scripture terms in unscriptural senses (§ 1). They have already been refuted by the proof that Christ is the true and coeternal Son; and Hilary now advances to the proof of the true Divinity of Christ, which is logically inseparable from His true Sonship (§ 2). But the danger is great lest, in attacking one heresy, he should use language which would sanction others (§ 3). Yet the truth is one, while heresies are manifold. Each of them can be trusted to demolish the others, while none can establish its own case. He illustrates this by the mutually destructive arguments of Sabellius, Arius and Photinus (§§ 5-7). Christ is proved to be God by the name God which is given Him in Scripture: The Word was God (§§ 8, 9). The name is His in the strict sense, and not any derivative meaning (§§ 10, 11). Yet Father and Son are not two, but one God (§ 13). Being the Son of God, He has the nature of God, and therefore is God (§§ 14-17), and yet not one Person with the Father (§ 18). Again, His power, manifested in His works, proves His Godhead (§ 19), as does the fact that all judgment has been given Him by the Father (§ 20). Christ's own words display the truth (§ 21). The Arians are blind to the plain sense of Scripture, and are more blasphemous than the Jews; Christ's reply to the latter meets the objections of the former (§§ 22-24). He asserts His unity with the Father (§ 25), and makes His works the proof (§ 26). The Father is in the Son and the Son is in the Father (§ 27): this is illustrated by the transmission of physical properties from parent to child and from flame to flame (§§ 28-30). In fact, the Catholic is the only rational explanation of the words of Scripture (§§ 31, 32). Again (§§ 33-38), the way to the Father is through the Son, and knowledge of the Son is knowledge of the Father. This would be impossible, were not the Son God in the same sense in which the Father is God. Thus the contrary doctrines of Sabellius and of Arius are confuted; there is neither one Person, nor yet two Gods (§§ 39, 40). Christ calls upon us to believe the truth, and belief is not only possible but reasonable (§ 41).
Book VIII. Piety is necessary in a Bishop, but he needs also knowledge and dialectical skill in the face of such heresies as were rampant in Hilary's day; for the heretics outdo the orthodox in zeal, and are masters in the art of devising pitfalls for the unwary reasoner (§§ 1-3). He maintains (§ 4) that hitherto he has established his case; and now turns, in § 5, to the Arian interpretation of I and the Father are One, as meaning that They are one in will, not in nature. The fallacy of this is shewn by a comparison of the unity of Christians in Christ (§§ 7-9); a unity which is confessedly one of nature, yet is not more natural than that of Father and Son, of which it is a type (§ 10). And indeed the words, I and the Father are One, are ill-adapted to express a mere harmony of will (§ 11). This gift of unity of nature could not be given, as it is, through the Incarnation and the Eucharist, to Christians, unless the Givers Themselves possessed it; i.e. unless Father and Son were One God (§§ 12-14). As a matter of fact, we have a perfect union, through the mediation of Christ, with the Father; and it is a unity of nature, a permanent abiding; an assurance to us of the indwelling of Father in Son and Son in Father, and of the fact that Christ is not a creature, one in will with the Father, but a Son, one in nature with Him (§§ 15-18). For, again (§§ 19-21), the Mission of the Holy Ghost is jointly from the Father and the Son; He is called sometimes the Spirit of the Father, sometimes the Spirit of the Son, and this is a further proof of the unity in nature of Father and Son. Hilary now enquires (§§ 22-25) into the senses in which Scripture speaks of the Holy Spirit. Sometimes this title is given to the Father, sometimes to the Son, in both cases to save us from corporeal conceptions of God. But it is also used, in the strict sense, of the Paraclete, as on the day of Pentecost. Now the Divine Spirit dwells in Christians; but this Spirit, whether styled the Spirit of God, or the Spirit of Christ, or the Spirit of Truth, proceeding from the Father and sent by the Son, is only one Spirit. Hence the Godhead is One, and the nature of the Persons within that Godhead one also (§§ 26, 27). He next points out (§ 28) that the Arians are inconsistent in worshipping Christ, and yet styling Him a creature; for thus they fall under the curse of the Law, and forfeit the Holy Spirit. Again (§§ 29-34) the powers and graces bestowed by God are described indiscriminately as gifts of one or another Person in the Godhead. The Son, therefore, as a Giver, must be one with the Father, Who is also a Giver, and one with the Spirit. There is One God and One Lord (§ 35); if we deny that the Son is God, we must also deny that the Father is Lord; which is absurd. They are One God, with one Spirit, but not one Person (§ 36). St. Paul expressly says that Christ is God over all; an expression which must, like all the Apostle's teaching, bear the Catholic sense, and is incompatible with Arianism (§§ 37-39). The supporters of Arianism are thus alien from the faith (§ 40). After a restatement of the truth (§ 41), Hilary proceeds to deduce the Divine nature of the Son from the fact that He has been sealed by the Father (§§ 42-45). This sealing makes Him the Father's counterpart, Whose Image He thus becomes, though in the form of a servant. If He were thus the Image of God after His Incarnation, how much more before that condescension (§ 46). In § 47 he again denies that this teaching reduces the Father and the Son to one Person; and then (§§ 48-50) works out the sense in which Christ is the Image of God. It means that They are of one nature and of one power, and that the Son is the Firstborn, through Whom all things were created. But creation and also reconciliation is the joint work of Father and Son (§ 51). Christ could not have stated more explicitly than He has done His unity with the Father; the recognition of this truth is the test of the true Church (§ 52). Heresy is blind to the essential difference between the life-giving Christ and the created universe, which owes its life to Him (§ 53). In Him dwells the whole fulness of the Godhead bodily. The Indweller and the Indwelt are Both Persons, yet are One God; and the whole Godhead dwells in Each (§§ 54-56).
Book IX. After a summary (§ 1) of the results already obtained, Hilary returns, in § 2, to certain of the Arian proof-texts, and warns his readers that their life depends on the recognition in Christ of true God and true man, for it is this twofold nature which makes Him the Mediator (§ 3). Universal analogy and our consciousness of the capacity to rise to the life in God convince us of these two natures in Him, Who makes this rise possible (§ 4). But heresy lays hold of words spoken by Christ Incarnate, appropriate to His humility as Man, and assigns them to Him in His previous state; thus they make Him deny His true Godhead. But His utterances before the Incarnation, during His life on earth, and after His return to glory, must be carefully distinguished (§§ 5, 6). Hilary now examines the aims and achievements of Christ Incarnate, and shews that His work for men was a Divine work, accomplished by Him for us only because He was throughout both God and Man, the two natures in Him being inseparable (§§ 7-14). After reaching this conclusion from a general survey of Christ's life on earth, he examines in the light of it the Arian arguments from isolated words. They assert that Christ refused to be called Good or Master. He refused neither title, and yet declared that both belong to God only (§§ 15-18). And, indeed, He could not have associated Himself more closely than He did with the Father, while yet He kept His Person distinct (§ 19). The Father Himself bears witness to the Son; and the sin and loss of the Jews is this, that, seeing the Father's works done by Christ, they did not see in Him the Son (§§ 20, 21). The honour and glory of Christ is inseparable from that of God (§§ 22, 23). The Scribe did well to confess the Divine unity, but was still outside the Kingdom because He did not believe in Christ as God (§§ 24-27). Next, the Arian argument from the words, This is life eternal, that they may know Thee, the only true God, and Jesus Christ Whom Thou hast sent, is refuted by comparison with cognate passages (§§ 28-35). For, indeed, if the Father be the only true God, the Son must also be the only true God (§ 36). That Divine nature which is common to Father and Son is subject to no limitations, and the eternal generation can be illustrated by no analogy of created things (§ 37). Christ took humanity, and, since the Father's nature did not share in this, the unity was so far impaired. But humanity has been raised in Christ to God; and this could only be because His unity in the Divine nature with the Father was perfect. Otherwise the flesh which Christ took could not have entered into the Divine glory (§ 38). There is but one glory of Father and of Son; the Son sought in the Incarnation not glory for the Word but for the flesh (§§ 39, 40). The glory of Father and Son is one; in that unity the Son bestows, as well as receives, glory (§§ 41, 42), and this glory, common to Both, is evidence that the Divine nature also is common to Both (§ 42). Again, the Arians allege the words, The Son can do nothing of Himself, which Hilary shews, by an examination of the context, to be a support of the Catholic cause (§§ 43-46). The Son does the Father's work, not under compulsion as an inferior, but because They are One. His will is free, yet in perfect harmony with that of the Father, because of their unity of nature (§§ 47-50). The Arians also appeal to the text, The Father is greater than I. The Father is, in fact, greater, first as being the Unbegotten, and secondly inasmuch as the Son has condescended to the state of man, yet without forfeiting His Godhead (§ 51). But He is not greater in nature than the Son, Who is His Image; or rather, the Begetter is the greater, while the Son, as the Begotten, is not less than He, for, although begotten, He had no beginning of existence (§§ 52-57). Next, the allegation of ignorance, based on St. Mark xiii. 32, and therefore of difference in nature from God Omniscient is refuted (§§ 58-62), both by express statements of Scripture and by a consideration of the Divine character. It is only in figurative senses that God is stated in the Old Testament sometimes to come to know, sometimes to be ignorant of, particular facts (§§ 63, 64). And so it is with Christ; His ignorance is but a wise and merciful concealment of knowledge (§§ 65-67). Yet the Arians, though they admit that Christ, being superior to man, knows all the secrets of humanity, assert that He cannot penetrate the mysteries of God (§ 68). But Christ expressly declares that He can and does, for Each is in the Other and is mirrored in the Other (§ 69). The ignorance can be nothing but concealment. Only the Father knows, i.e. He has told none but the Son; the Son does not know, i.e. He wills not to reveal His knowledge (§§ 70, 71). God is unlimited; unlimited therefore in knowledge. The nature of Father and Son being one, it is impossible that the Son should be ignorant of what the Father knows. As in will, so in knowledge, They are One (§§ 72-74). And the Apostles, by repeating their question after the Resurrection, shew that they were aware that His ignorance meant reserve. And Christ did not, this time, speak of ignorance, though He withheld the knowledge which they asked (§ 75).