The article examines the Johannine foundation of the Encyclical Deus Caritas Est. It shows how Benedict XVI drew heavily on the Augustinian exegesis of the Johannine literature (with a particular focus on the First Epistle of John). The analysis follows the three fundamental elements that the Pope identifies at the beginning of the document, comparing the texts of the two authors (St. Augustine and Benedict XVI): the lexical clarification of eros and agape, the interaction between the love of God and the love of neighbor, and finally the pneumatological foundation of love. Then, starting from this last element, the article proposes to interpret the second part of the Encyclical as a pneumatological ecclesiology that the Pope presented to the Church at the beginning of his pontificate.