Gospel Guidebook: Getting and Keeping It Right 
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Review of Simply Trinity by Matthew Barrett
by Robert P. TerryUpdated September 8, 2025
The title of the book "Simply Trinity: The Unmanipulated Father, Son, and Spirit" by Matthew Barrett is misleading and ironic. It's misleading because the author does not mean simple-to-understand Trinity. It's ironic because, as a polemic, he might think he is not manipulating the Father, Son, and Holy Spirit, but he is definitely trying to manipulate his readers into believing that the nature of God is neither modalistic nor tritheistic, despite making the case for modalism and revealing his own tritheism.
Does the author establish modalism? I think so. The author explains that God has only one will, but he tries hard to distance himself from modalism (i.e., the boogeyman of Sabellianism, which he mentions over 40 times in the book, referring to it on page 145-146 to describe a caricature of modalism in which God supposedly sequentially switches roles, sometimes being the Father, sometimes the Son, and sometimes the Holy Spirit, a teaching regarding which there is no firm evidence anyone at anytime in church history has ever believed, since the only thing we know of Sabellius is what his enemies wrote of him). The author's efforts reveal (perhaps unknowingly to him) his insecurities regarding modalism. For example, he wastes no time calling Sabellianism a heresy (p. 58), knowing that using a big, scary word like Sabellianism and calling it a heresy is sure to prejudice the minds of his readers. However, he does know something of it (despite having a skewed understanding of it), something of its power that must make him afraid of it. This seems evident in chapters 6 and 7 where he spends over 50 pages trying to defend the doctrine of the eternal generation of the Son, a doctrine by which the trinity stands or falls. He says, "Without generation, we fall head first into Sabellianism, for what previously distinguished Son from Father is dissolved, and as a result the persons are conflated until there is no plurality of persons at all" (p. 163). Along the same lines he quotes John Gill and Athanasius (p. 163-164). With this admission, the author takes the burden of proof upon himself to demonstrate that the validity of the doctrine of the eternal generation of the Son. Regrettably, for him, he fails miserably. He doesn't quote a single Bible verse as proof of the doctrine, and he admits this on page 183. Instead, he bombards the reader with quotes from his "dream team" of trinitarian theologians (more on this below), gives us eisegesis of passages that can clearly be interpreted otherwise, makes assertions and draws conclusions that don't follow (i.e., non sequitur), and employs circular reasoning. But having already admitted that there is not a single proof text of the doctrine, his efforts to prove it through these other means just don't suffice. As a result, I can only conclude that Sabellianism stands, for according to the author, we have fallen head first into it.
Does the author reveal a belief in tritheism? Again, I think so. He spends a lot of time discussing how these three persons of the Trinity can individually appropriate actions to themselves according to their own personal properties, but often feels the need to tell us that he is not teaching tritheism (i.e., the three-headed monster of social trinitarianism, which he mentions over 70 times in the book, and supposes to refute by appealing to "simplicity," even going so far on page 137 to say he believes in "absolute simplicity," not seeming to realize that "absolute simplicity" requires modalism because it precludes any and all distinctions in God). For example, on page 309 he keeps emphasizing (at least four times) that what he is teaching is not polytheism (i.e., that God has three wills, separate wills, anything but one will). There would be no need to labor as hard as he does if he were not teaching something that sounds just like tritheism. But as the saying goes: if it looks like a duck, walks like a duck, and quacks like a duck, then it's a duck. Let me further substantiate my claim in the following paragraphs.
The author spends a whole chapter denouncing social Trinitarianism (p. 67-94), but then strangely spends several pages affirming the "covenant of redemption" (p. 305-310) wherein the Father and Son supposedly had intratrinitarian dialogue with each other in eternity. But as mentioned above, he assures us that this is not polytheism. How does he do this? He just asserts it, appeals to John Owen, and invokes the power of technical terms (more on this below). This is the author's standard operating procedure because, according to him, "there is no verse in the Bible that spells out the Trinity," "every heretic has a Bible verse," and "radicals and rationalists" appeal to the Bible only (p. 35-36). But don't despair dear reader, because in place of the Bible, he has his "dream team" of trinitarian theologians, which unsurprisingly doesn't include any of the prophets or apostles, to come to his aid with a toolbox of big words at his disposal (p. 34).
The author loves to throw dust in the eyes of his readers by invoking technical terms. He invokes them often enough that the reader could become hypnotized by them if not careful. As to their exact meaning, he never sufficiently explains them, at least not in a way that could substantiate the claims he is trying to prove with them. As for the covenant of redemption mentioned above, he asserts that it does not involve multiple wills in God because of "appropriation," but never explains appropriation in a manner that could exonerate him from the charge of tritheism.
More specifically, he says, "Properly understood, the covenant of redemption does not violate the one, simple will of our triune God, but shows us how the eternal relations of origin, which alone distinguish the persons, extend themselves, corresponding to each person’s appropriation of that one will in the many layers of redemption" (p. 310). Besides begging the question (i.e., assuming his conclusion in his premise), this sentence contains several technical terms, including "eternal relations of origin", "person," and "appropriation." The author provides a glossary at the end of the book, but defines these technical terms by using other technical terms that are, in turn, defined by the very same technical terms in question. For instance, just see his definitions for "eternal relations of origin," "person," and "subsistence" (p. 321-325). It's like going to location A and being told to go to location B, and then going to location B and being told to go back to location A.
Apart from the technical terms, however, the above sentence doesn't even make sense. First he says that the eternal relations of origin alone distinguish the persons, but then says that they extend themselves to correspond to each person's appropriation of the one will. So which is it? Do the eternal relations of origin alone distinguish the persons or can they extend themselves to correspond to another distinguishing feature called appropriation? On the other hand, if he should say that appropriation is merely an extension of the eternal relations of origin, then how does appealing to appropriation defeat the charge of tritheism? The charge remains because, instead of some exonerating concept called appropriation, he now has the eternal relations of origin acting like three gods themselves under the name of appropriation. He did try to explain the relationship between eternal relations of origin and appropriation differently on page 224, but it's non sequitur. There is nothing in his explanation (or definition of eternal relations of origin on page 321) by which we can deduce some exonerating concept of appropriation. And, again, if appropriation is simply a facet of the eternal relations of origin, then he has said nothing to defeat the charge of tritheism by using this word. Plus, what he explains on page 224 as pertaining to the economic trinity, he is now trying to apply to the immanent trinity. It is utter confusion.
In the end, what the author calls "Simply Trinity" seems to be nothing more than wavering between two opinions (1 Kings 18:21). "If the LORD be one, then follow Him, but if three, then follow them." The modalists and social trinitarians are hot and cold, respectively, but the author's Trinitarianism is lukewarm and must be spit out.