David Vopřada demonstrates that Ambrose of Milan's Expositio in Psalmi CXVIII was a mystagogical work aimed at deepening his audience's awareness of the meaning of their baptism and its significance in their daily lives. The first section of the book presents a thorough overview of mystagogical literature in the patristic period in general and in Ambrose's work. The second section argues for the mystagogical character of the Expositio. Vopřada singles out Ambrose's Expositio as remarkable in its time as a work aimed at deepening the catechesis given to the newly baptized, an approach to explaining Christian mysteries that would not reappear until Maximus the Confessor. Taking a more holistic approach to understanding mystagogy, the book argues for the disciplina arcani in Ambrose as focused on more than merely the details of Baptism. Rather, the arcanum is the intra-Trinitarian life and the operation of Christ in every aspect of the life of the baptized, inasmuch as the Christian life constitutes a participation in the life of Christ and the Trinity in a manner that cannot be explained theoretically to one who lacks the eyes of faith but must first be experienced to be understood. The third section of the work considers how Ambrose attempts to deepen his audience's awareness of the mystery of Christ in three areas: the sacraments of Baptism, Eucharist, and Penance; the daily life of the Christian; and the historical situation of his local Milanese audience, which encountered various groups that denied the divine Sonship of Jesus, namely pagans, heretics, and Jews. Those who persecute David in Psalm 118 are presented in the Expositio as figures of the Christian struggle in Ambrose's own time and the struggle with these groups is presented as making more fully clear the truth of the faith held by Ambrose's congregation. Vopřada provides a thorough and fascinating consideration of Ambrose's vision of the world as presented in the Expositio worthy of the attention of anyone interested in Ambrose or late antique mystagogy.