Hilary of Poitiers (ca. 315-367) was born ca. A.D. 315 at Poitiers in Aquitaine.[1] Often called the “Athanasius of the West,” Hilary was a well-educated convert from paganism who became Bishop of Poitiers between A.D. 353-354.[2] Hilary experienced an array of challenges and difficulties throughout his life and ministry, including a four-year exile to Phrygia imposed by the Roman Emperor Constantius II.[3] His contributions during the Council of Seleucia in A.D. 359 established his reputation as one of the leading theologians of his era.[4] In addition to his best-known works, De Trinitate, De Synodis, and Opus Historicum, his other writings include commentaries on Matthew and the Psalms.[5]
Hilary of Poitiers’s de Trinitatis, or The Trinity, is the bishop’s theological magnum opus. Divided into twelve books within the entirety of the work, The Trinity sets forth a comprehensive and orthodox overview of the doctrines of the triune God. Written during his exile by Constantius II for refusing to condemn Athanasius, the work is the first major attempt to provide a comprehensive expression of Nicene Trinitarian orthodoxy in Latin. Hilary understood the triune God to be one divine essence in three persons. This forms the central thesis of his work.
Hilary wrote The Trinity to combat the Arian heresies that had not only gained influence but also tremendous power in his day. Though Arians are explicitly mentioned by name only twice in the work, they are far more frequently referenced using phrases such as “the new teachers of Christ,” “the heretics of the present day,” and “the new apostolate of anti-Christ.” While the context of these references to the Arians identifies them as such, Hilary’s use of such theologically charged and startling phrasing also emphasizes in bold terms the nature of Arianism as heresy and the clear danger emanating from Arian views. As far as scholars are aware, no individual asked Hilary to write The Trinity. Rather, Hilary wrote this extraordinary work as a fulfillment of the obligation of his office as a bishop: to faithfully preach the Gospel. In light of this, Hilary’s work in The Trinity can be understood in a dual sense as both a response to the heresies of his day and a treatise articulating the orthodox doctrine of the Trinity.

Book 1 of The Trinity constitutes an overview of the author’s purpose in writing the treatise. Hilary established two purposes for writing the work. First, Hilary wrote to correct the Arian heresies that infected so many churches and ruling authorities during his era of ministry. Second, Hilary wrote The Trinity to advance the Gospel by articulating a comprehensive, orthodox understanding of the triune God. While these purposes are distinct, they are also interrelated. To oppose and refute heresy is a necessary and laudable objective for any theologian. However, the simple opposition and refutation of heresy along is insufficient; once a heretical doctrine is refuted, it must also be replaced with orthodoxy to provide the corrective theological remedy. Hilary states this objective up front in the first book. Book 1 also includes a concise overview of the remaining eleven books of the work (Books 2 through 12), providing the reader with an advance framework of the content, objectives, and central arguments of each book.
Book 2 constitutes a simple summary of Hilary’s trinitarian theology. In this sense, Book 2 is a framework which shapes the remainder of the books, as well as a standalone articulation of Nicene orthodoxy which Hilary intended to be readily accessible to the reader. As Hilary stated, “from the statement that are made they will realize very clearly that the true nature is appropriate to the name and the name to the true nature” (20).
Book 3 builds on the theological foundation laid by Hilary in Book 2. In Book 3, Hilary deals with the challenging and mysterious nature of Trinitarian theology and the difficulty human beings have in comprehending the revelation of the triune God. The bishop homed in on the words of Jesus, “I in the Father and the Father in me,” as an example of God’s ultimate expression of His own omnipotence. Further, Hilary acknowledged that the limitations of the human mind in grasping the magnificent doctrines of the Trinity, but also advanced the remedy of faith.
Book 4 provides a direct confrontation with the Arian heresies and those church leaders advancing them. Hilary provides a description of the heretical views held by Arian Christians, including the Roman Emperor Constantius II who would ultimately banish him from Poitiers, and demonstrates the errant nature of Arianism by comparing Arian beliefs to the orthodox doctrine of the Trinity. While Arians believed in the one true God, they did not believe in the Nicene understanding of God’s triune character: one essence in three persons. Arians denied the divinity of Christ as being co-God with the Father. Hilary asserted that Arians were marked by a lack of faith evident in their failure to accept and proclaim the God as both the Father and the Son.
Book 5 continues the refutation of the Arian heresies. Hilary noted that the organization of Book 5 reflects the order which the Arian heretics adopted in their presentation of their beliefs. That is, Hilary confronts and refutes the heretical Arian doctrines point-by-point in his reply. Hilary provides a step-by-step presentation of orthodoxy, refuting the errors of the Arians in failing to accept the deity of Christ while simultaneously avoiding the errors of tritheists by defending the oneness of God. Nicene orthodoxy is one divine essence in three persons, and Hilary advances this view faithfully. It should also be noted that while Hilary provides relatively little discussion of the Holy Spirit, as the focus is primarily upon defending the deity of Christ, the Spirit is also clearly in view in the orthodox doctrines Hilary defends and advances.
Book 6 identifies the deceptive and even theologically cannibalistic nature of the Arian heretics to which Hilary responds. Hilary exposed the tendency of the Arian heretics to turn on their own heretical brethren from other errant camps (namely, Valentinians, Sabellians, Manians, and Hieracasians) by refuting their wrong views and claiming other orthodox doctrines of the church as a disguise for their own heterodoxy.

Book 7 continues the approach of refuting heretical positions and deals specifically with the errant teachings of Sabellius and Ebion. In evaluating the views of each heretic, Hilary examines both that which is wrong and that which is correct. As is typically the case in heterodoxy, the heretical articulations are not purely error, but rather a mixture of error and truth. Hilary acknowledged the seductive and dangerous nature of this tendency and rightly divides the truth from the error in each view.
In Book 8, Hilary acknowledged the foundation established in the previous 7 books as being sufficient to advance to a deeper examination of the evidence for one God. While much of Hilary’s emphasis has been on the defense of Christ’s deity, Book 8 provides a robust defense of the oneness of God. After defending the Nicene doctrine of God’s oneness, Hilary returns to a full-throated refutation of his heretical opponents in Book 9 who deny the divine nature of the Son.
Book 10 continues a defense of the deity of Christ by refuting the distortions of Jesus’s Passion and statements made by the Lord during His Passion by the Arians. Book 11 contains Hilary’s confrontation of the error of subordinationism. Hilary denied that there is any sense of weakness within the Godhead (that is, that the Son is subordinate to and thus weaker than the Father) and affirmed the full deity both the Father and the Son within the Godhead. Along with affirmation of the deity of the Holy Spirit, this doctrine is a hallmark of the Nicene orthodoxy Hilary advanced.
Finally, in Book 12, Hilary concludes his magnificent work on the Trinity by invoking the guidance of the Holy Spirit in affirming the divinity of both the Father and the Son. In Book 12, Hilary continues to defend the eternal relations of origin of both the Father and Son and their identity as distinct Persons with the same divine nature. Nicene orthodoxy is incomplete without an affirmation of the divinity of all three Persons. One God in three persons: this is Nicene orthodoxy advanced and defended by Hilary of Poitiers.
[1] Hilary of Poitiers, The Trinity, trans. Stephen McKenna, The Fathers of the Church: A New Translation (Washington, D.C.: The Catholic University of America Press, 2002), V.
[2] F. L. Cross and Elizabeth A. Livingstone, eds., The Oxford Dictionary of the Christian Church (Oxford; New York: Oxford University Press, 2005), 774; Hilary of Poitiers, The Trinity, V.
[3] F. L. Cross and Elizabeth A. Livingstone, eds., The Oxford Dictionary of the Christian Church (Oxford; New York: Oxford University Press, 2005), 774.
[4] F. L. Cross and Elizabeth A. Livingstone, eds., The Oxford Dictionary of the Christian Church (Oxford; New York: Oxford University Press, 2005), 774.
[5] F. L. Cross and Elizabeth A. Livingstone, eds., The Oxford Dictionary of the Christian Church (Oxford; New York: Oxford University Press, 2005), 774.