Thomistic Mystagogy: St. Thomas Aquinas's Commentaries on the Mass

Urban Hannon. Thomistic Mystagogy: St. Thomas Aquinas’s Commentaries on the Mass. Os Justi Press, 2024.

Reviewed by Brandon L. Wanless, Ph.D., Assistant Professor of Dogmatic Theology, The Saint Paul Seminary, University of St. Thomas (St. Paul, MN).


Anyone who reads the 83rd question of the tertia pars of the Summa theologiae knows that St. Thomas Aquinas understands the liturgy of the Mass to be, as it were, a school of religion with each action and line serving to dispose participants to right reverence and devotion and thus to acts of charity. On this score, Aquinas would be an advocate for the full and conscious participation called for by Vatican Council II (cf. Sacr. Conc. §14), in which mental latria is the telos of all external bodily worship (cf. ST II-II 81.7).

It is with grateful enthusiasm, therefore, that one reads through Urban Hannon’s recent Thomistic Mystagogy. It is a handy little volume—measuring only five inches wide—small enough to fit in one’s hand, and short enough to get through in one sitting—less than 100 (small) pages, exempting the appendices. 

Hannon confidently leads us through Aquinas’s own “liturgical lectio divina” (98) by tracing the Angelic Doctor’s divisiones and expositiones Missae found in the tertia pars as well as in his commentary on the fourth book of Peter Lombard’s Sentences. Hannon masterfully makes accessible Aquinas’s mystagogy on the sacred liturgy of the Mass, “that is, his theological teaching on the meaning and purpose of its various rites, for the sake of helping his fellow Christians better understand the mysteries they celebrate” (5). Liturgy itself as external acts consists of both things that are said and things that are done, and Aquinas gives careful attention to both the many words and the many actions of the liturgy. He thinks of the liturgy as supplemental though essential to the corresponding sacraments that they accompany. More than the “mere being” of the sacrament, liturgy concerns the “well-being” of the sacrament in its ritual usage (6). 

Hannon not only faithfully presents Aquinas’s commentaries on the Mass from In IV Sent., dd. 8 & 12 as well as from ST III, q. 83, but also explains what is rather tersely exposited by Aquinas. He does this first with a fourteen-page chapter on Aquinas’s divisiones Missae, followed by a second chapter on Aquinas’s expositiones Missae that accounts for almost 70 of the book’s 98 pages. It is admirable that Hannon consistently compares and contrasts throughout the overwhelmingly complementary accounts given in the Scriptum and in the Summa. His effort “to piece together a properly Thomistic commentary on the Mass” (7) is clearly successful.

The appendices themselves are a nice addition: the first provides the four principal primary texts, two each from the Scriptum and the Summa; in the second, Hannon provides a very helpful set of charts, two of which serve as roadmaps through the divisiones and expositiones Missae given in the four texts of the first appendix.

Hannon seems to be intentional in refraining from offering too much of his own thoughts. One does not want to overexplain nor simplify the liturgical meaning of any one act or word of the Mass, let alone the entirety of the rite—as Hannon puts it—“not only because the richness of the form should fit the richness of the content, but also because an easier text would not hold our attention anyway” (97). Liturgy itself is intentionally difficult to comprehend; intrinsic to it is a tension between the mysterious and a rational accessibility.

It is surely not exaggeration to say that this text is an exercise in correction, both with respect to Thomistic thought and with respect to liturgical theology. For the former, Hannon notes that while Aquinas is “rarely associated with liturgical prayer” (3), in reality he “takes the rites of the Mass tremendously seriously” (93). As for liturgical studies, rarely is Aquinas even considered, let alone considered authoritative. To be fair, his commentaries are far from innovative; Hannon notes, “St. Thomas is rarely an altogether original thinker, nor is he trying to be” (8n14). And this is precisely the point—Hannon takes issue with modern attempts at liturgical positivism and simplification that he dubs “vulgarization” (97). 

It makes for a difficult task to review a book that contains no material ambiguities, let alone any asserted errors whatsoever; that is, I agree with everything I read. Hannon clearly has contemplated carefully, deeply, and regularly how Aquinas considers the intricate words and actions of the Mass; undoubtedly, he has done the same for the liturgy itself. 

If there is a criticism to present, it is precisely that the text is too short. The Conclusion ends and leaves one wanting more. The desire for more mystagogy is indeed the sign of a good mystagogy. Hannon puts to use the discipline of the secret (cf. ST I 1.9 ad 2), exercising reservation from expounding much more than what Aquinas himself offers between the four texts of the Scriptum and the Summa. Hannon’s restraint is commendable, especially since this reviewer might not have settled for so limited a scope. A student of Aquinas’s theology would indeed know that simply examining a few focused articles of the Common Doctor’s corpus does not completely exhaust his account of a subject. No, instead, little insights into his liturgical theology are to be found all throughout the Summa, for instance, among the many replies to objections, or tucked away in his scriptural commentaries; one thinks especially of 1 Corinthians 11. On this score, Hannon does integrate a few features of Aquinas’s sacramental theology from earlier in the tertia pars in his Introduction. However, this reviewer would have appreciated more from the treatise on Divine Law or the virtue of religion in the secunda pars. Much more could have been said, even briefly, regarding Aquinas’s accounts of signification, the relation between external and internal worship, and the differences between the Old and the New Law rites. Hannon himself admits that the book is intentionally limited in scope; in fact, half of his Conclusion concerns further studies that could be pursued, admitting that there is material yet in the tertia pars and even the Summa contra Gentiles to be mined. 

Given its simplicity, not to mention sizable margins and beautiful font, the book would make for a fine study text even for a popular audience, especially those attached to traditional Catholic liturgy, particularly Mass in the usus antiquior. (The Mass of Aquinas’s day materially aligns much more closely to the extraordinary form of the Roman Rite than to our contemporary novus ordo.) Although Hannon obviously has the scholarly wherewithal, Thomistic Mystagogy seems intended less to advance the scholarly discussion than to remind us of what has been too easily forgotten recently about Aquinas’s thought and the Eucharistic liturgy itself.