This STL thesis, submitted in October 2019 at the Pontifical University of St. Thomas Aquinas (Angelicum), Rome, in partial fulfillment of the requirements for the Licentiate in Sacred Theology, investigates the theology of the rite of the Mass (Missae sacrificium) in St. Thomas Aquinas’s Summa Theologiae (III, q. 83), in comparison with De sacro altaris mysterio of Pope Innocent III and De mysterio missae of St. Albert the Great. The work offers a systematic theological reading of Aquinas’s Eucharistic doctrine and situates it within the broader medieval theological and liturgical tradition. Particular focus is placed on Aquinas’s theological method in the Summa Theologiae: a systematic contextualization demonstrates the analogical application of the principles of Sacra Doctrina to Sacred Scripture, sacramentology, and the liturgical rites of the Holy Mass. The spiritual senses of Sacred Scripture are shown to correspond analogically to spiritual senses in the liturgy. The study integrates Aquinas’s doctrine of anthropology, epistemology, his theory of the human act and religion, general sacramentology, scriptural and eucharistic signification, and his mystagogical Expositio Missae in Summa Theologiae III, q. 83, a. 4–5 on the Eucharistic celebration of the Mass. In its main section, the thesis examines Aquinas’s mystagogy of the Eucharistic liturgy by following the structure of the contemporary Roman (Curial) Ordo Missae presupposed in Summa Theologiae III, q. 83, a. 4 and 5, in comparison with Pope Innocent III—whose De sacro altaris mysterio exercised major influence on 13th-century liturgical spirituality—and with the De mysterio missae of St. Albert the Great, whose approach illustrates an alternative model of liturgical mystagogy. A historical-theological contextualization traces the development of liturgical exegesis to two distinct yet overlapping currents of medieval theology: a philologico-theological school represented by figures such as Florus of Lyon and St. Albert the Great, and a symbolic-spiritual school represented by Innocent III and Thomas Aquinas. The analysis demonstrates how Aquinas’s systematic parallelization of scriptural, sacramental, and eucharistic signification resolves the classical theological problem of articulating the spiritual sense in the liturgy. The thesis was submitted for the Thomistic Section of the Faculty of Theology for the Lectio coram held on 3 October 2019. It belongs to the fields of Thomistic and systematic theology, with contributions to Thomistic philosophy, liturgical history, fundamental theology, and in particular sacramental and liturgical theology. It was subsequently expanded into the doctoral dissertation (defended in 2023) and finally published in its definitive monograph form in 2025 (ISBN 978-3-8306-8297-4). Final Published Monograph Dominik Pascal Witkowski, The Sacramental Signification in the Rite of the Holy Mass. The Synthesis of St. Thomas Aquinas in Comparison with Pope Innocent III and St. Albert the Great, Dissertationen. Theologische Reihe, vol. 122, EOS Verlag Sankt Ottilien, 2025. ISBN 978-3-8306-8297-4. Publication and Priority Notice (2025 Revision) This document constitutes the original scholarly work submitted in partial fulfillment of the requirements for the Licentiate in Sacred Theology (STL) at the Pontifical University of St. Thomas Aquinas (Angelicum), Rome, on 3 October 2019. It represents the first public and citable formulation of the synthetic and comparative theological framework concerning the sacramental signification in the rite of the Holy Mass according to the thought of St. Thomas Aquinas, in dialogue with Pope Innocent III and St. Albert the Great. A substantially revised and expanded version of this research was subsequently completed, defended, and approved as a doctoral dissertation on 22 September 2023 at the same academic institution, and is now formally published in its definitive monograph form as cited above. This 2019 STL thesis establishes the chronological priority of the author’s theological findings and contains the earliest occurrence of several concepts, comparative structures, historical analyses, and graphical representations relating to Thomistic sacramental theology, which were later further developed and presented in their definitive form in the published doctoral monograph. Citation Notice Scholars who make use of the thematic presentations, concepts, analytical frameworks, or diagrams first appearing in this thesis are required, in accordance with academic standards of attribution and research integrity, to cite this publication and, where relevant, the final published monograph (ISBN). Scholarly Transparency The inclusion of this version in the public domain ensures the preservation of academic transparency and historical development. Certain themes that have appeared in theological publications from 2022 onwards were first formulated in this 2019 thesis. This document therefore represents the earliest publicly documented version of insights that have informed later scholarly discussion in this field. Version Information This is Version 2 of the Zenodo record, updated in 2025 to provide bibliographic linkage to the published monograph and to ensure full scholarly transparency. A final and revised scholarly edition with minimal editorial corrections is being prepared as version 3.