On the Sacrament of the Altar

William of St. Thierry composed this treatise on the Eucharist around 1130, during a period of intense theological development in the early twelfth century. As abbot of the Benedictine monastery of St. Thierry near Reims, William wrote in response to emerging controversies about the nature of Christ's presence in the sacrament, particularly following the earlier disputes sparked by Berengar of Tours. The work reflects the Cistercian reform movement's emphasis on returning to patristic sources while engaging contemporary theological questions about sacramental reality.

The treatise presents a sophisticated account of eucharistic theology that draws heavily on Augustine while incorporating insights from the Greek Fathers, especially John Chrysostom. William argues that the Eucharist effects a real transformation both in the elements and in the faithful communicant, emphasizing the mystical union between Christ and the believer accomplished through sacramental participation. He develops a carefully nuanced position on the mode of Christ's presence that avoids both crude materialism and mere symbolism, insisting that the sacrament operates through divine power rather than natural processes. The work integrates sacramental theology with William's broader understanding of spiritual ascent, presenting the Eucharist as both the culmination of liturgical worship and the foundation for contemplative union with God.

De sacramento altaris became influential among Cistercian writers and contributed to the development of scholastic eucharistic theology in the generations following William. The treatise demonstrates the sophisticated theological reflection occurring in monastic centers during the twelfth-century renaissance, bridging patristic tradition and emerging scholastic method. Who should read this: students of medieval sacramental theology and historians of Cistercian spirituality will find William's synthesis of mystical and theological approaches particularly valuable, though readers seeking devotional rather than doctrinal treatment of the Eucharist should look elsewhere.