Aquinas’s role in compiling the Corpus Christi liturgy, to include the composition of the antiphons and poetic texts, is now better appreciated by laity and scholars alike, many of whom find in the beloved hymns commonly sung at Adoration and Eucharistic Processions a beautifully edifying distillation of Saint Thomas’s teaching on the Blessed Sacrament. However, the place of this Office and Mass within the historical development of Aquinas’s doctrine on the priesthood and Eucharist is perhaps less acknowledged. The aesthetic and spiritual appeal of the hymns may tend to obscure the importance of the historical context which informs Aquinas’s unique compositional, poetic, and theological directions. Hidden behind the impressiveness of the Saint’s artistic execution, I argue, lies the rudiments of the well-developed doctrinal synthesis of priesthood and Eucharist articulated in Summa Contra Gentiles IV and Summa Theologiae III. In this essay, I look at sequence for Mass Lauda Sion Salvatorem and the hymn for Matins Sacris solemniis to show how, already in the Orvieto period (1261-1265), Aquinas points the way toward sacramental doctrines expressed with more precision not only in the two Summae, but in the dogmatic teaching of the Council of Trent on the sacraments of Eucharist and Holy Orders. I will also highlight the unique and even innovative nature of Aquinas’s positions by way of contrast with Saint Bonaventure’s sacramentology. I will conclude by offering some reflections, drawn from Aquinas’s synthetic treatment of Eucharist and Orders, on the inseparability of priestly renewal and Eucharistic revival.