Back on April 19, 2025 I published a new post under the title: Victor of Vita, the council of Carthage (484), the Book of the Catholic Faith, and the Johannine Comma (link). The thread delved into the history and controversy between two competing factions of professing Christians in North Africa—the homoians and homoousians—during the middle through late fifth century. This controversy between the homoians and homoousians began a full century earlier with promulgation of the Second Creed of Sirmium in 357 A.D.—also known as "The Blasphemy of Sirmium" (link).
Recently, my studies into the controversy between the homoians and homoousians has been renewed with my reading of Daniel H. Williams, Ambrose of Milan and the End of the Arian-Nicene Conflicts (link). Chapter 3, "Homoians and Anti Homoians: North Italy" (pages 69-103) is excellent; and in pages 96-103 Dr. Williams relates a fourth century apologetic work on the Trinity I had no memory of being mentioned in any my previous readings—De trinitate libri XII. From the pen of Dr. Williams we read:
Since the seventeenth century, the work commonly known as the De trinitate libri XII had been attributed to either Vigilius of Thapsus or Athanasius of Alexandria, since the latter's name appears as the author in the earliest and majority of manuscripts. Just before the turn of this century, careful manuscript studies by G. Ficker and G. Morin, showed that neither Vigilius nor Athanasius could have been the author, and that the most ancient and numerous manuscripts contain only seven books, not the twelve which Chifflet had compiled. While there does exist a longer recension which includes an eighth book, it is generally agreed that the first seven form a cohesive ensemble attributable to a single author. The latter five books are a comparatively recent agglomeration of treatises, noticeably different from the first seven in style and terminology. This consensus is reflected in the recent critical edition of the De trinitate (CCSL ix. 3-99), in which V. Bulhart treats books I-VII as a literary whole and prints the first (or shorter) and second recensions in parallel columns. But here the consensus ends. Regarding the questions of authorship and chronology for the De trinitate, scholarly opinion has been and continues to be sharply divided. With the publication of the CCSL edition (1957), Bulhart revived the view that Eusebius of Vercelli was the author of the first seven books (the first recension). [Pages 96-97]
He then writes:
Because of the imposing difficulties with the chronology and authorship of De trinitate, the contents of the treatise have been left virtually untreated by modern scholarship...As we shall see, the De trinitate provides one of the most informative glimpses into the evolution of Latin pro-Nicene literature, with the exception of those writings from Hilary and Ambrose. [Page 98]
After reading Dr. Williams book, I became somewhat obsessed with learning more about this "virtually untreated" work . I began with gathering information on the proposed authors of De trinitate libri XII: "Psuedo-Athanasius", "Vigilius of Thapsus", "Eusebius of Vercelli" and "Gregory of Elvira". Whilst engaged in some research on Vigilius of Thapsus, I discovered he is mentioned in one of the commentaries on 1 John that I own; note the following:
In PL 62, 237—334 there is a work De Trinitate consisting of twelve books. Formerly it was attributed to the North African bishop Vigilius of Thapsus who was present at the Carthage meeting; it has also been designated Pseudo-Athanasius; but other guesses credit it to a Spanish scholar such as Gregory of Elvira (d. 392) or Syagrius of Galicia (ca. 450). Recently the first seven books have been published (CC 9, 3—99) as the work of Eusebius of Vercelli (d. 371), but not without debate (see CPL #105). In any case, the work is probably of North African or Spanish origin; and its parts may have been composed at different times, e.g., Books 1—7 written just before 400, and 8—12 at a period within the next 150 years. In Books 1 and 10 (PL 62, 243D, 246B, 297B) the Comma is cited three times. (Raymond Brown, The Epistles of John, Appendix IV, 1982, p. 782)
Now, whoever actually wrote De trinitate libri XII—formerly attributed to Vigilius of Thapsus—the author(s), in defense of pro-Nicene Trinitarianism, cited the Johannine Comma. The following are the germane Latin texts from Migne’s Patralogia Latina, Volume 62 that were referenced by Brown (PDF):
Liber I 206 dirente Joanne evangelista in Epistola sua : Tres sunt qui testimonium dicunt in cælo, Pater, et Verbum, et Spiritus, et in Christo Jesu unum sunt (I Joan. v, 7) [Migne PL 62, p. 243D; Bulhart CCSL 9, p. 15]
English: John the Evangelist in his Epistle asserts: Three are they who bear witness in heaven, the Father, the Word, and the Spirit, and in Christ Jesus they are one
Liber I 209 Jam audisti superius evangel stam Joannem in Epistola sua tam absolute testantem : Tres sunt qui testimonium dant in cælo, Pater, Verbum et Spiritus sanctus : et in Christo Jesu unum sunt (I Joan. v, 7). [Migne PL 62, p. 246B; Bulhart CCSL 9, p. 19]
English: We have heard the superior gospel from John in his Epistle as absolute testimony: There are three that bear witness in heaven, the Father, the Word, and the Holy Ghost: and in Christ Jesus they are one
Liber X 281 et Joannes in Epistola sua ait : Tres sunt qui testimonium dicunt in cælo, Pater, Verbum et Spiritus : et in Christo Jesu unum sunt (I Joan. v, 7) [Migne PL 62, p.297B; Bulhart CCSL 9, p. 145]
English: and John in his Epistle says: There are three that bear witness in heaven, the Father, the Word, and the Spirit: and in Christ Jesus they are one
In addition to the three citations referenced by Brown, I found fourth citation of 1 John 5:7 in De trinitate libri XII:
Liber V 249 sicut
Joannes evangelista in Epistola sua tam absolute testatur : Et tres unum sunt (I Joan. v, 7). [Migne PL 62, p.274C; Bulhart CCSL 9, p. 77]
English: just as John the Evangelist testifies so
absolutely in his Epistle: And the three are one.
Now, most Patristic scholars are in agreement with Dr. Williams that only the first seven books of De trinitate libri XII were written by the same author, and that they were penned earlier than the other five. Following Bulhart’s assessment that it was Eusebius of Vercelli who wrote the first seven books, we have three clear citations of the Johannine Comma—in support of Nicene Trinitarianism—a full century before that of Victor of Vita.
Shall end this post with a Google AI Overview of Eusebius of Vercelli that I found useful:
Saint Eusebius of Vercelli (c. 300-371 AD) was a 4th-century Italian bishop, a staunch defender of orthodox Nicene Christianity against Arianism, known for establishing the first community of clergy living a monastic, communal life, and for enduring exile for his faith. Born in Sardinia, he became the first recorded bishop of Vercelli, unifying clerical and monastic ideals by having priests live together in piety, and bravely resisted Arian bishops at the Council of Milan, leading to his persecution and exile to the East. He returned after Emperor Julian's amnesty, working with St. Athanasius and Hilary of Poitiers to restore Catholic doctrine before his death in 371.
Grace and peace,
David