Summary: This article systematically reconstructs the mind of Saint Bonaventure concerning the Eucharist as a sacrament of communion because it preserves love of neighbor. He begins the reflection with a consideration of the situation of the members of the Mystical Body, but does not cease to take into account the condition particular to each believer. Analyzing the texts, one understand more clearly the concept of the sacrament and the identity of the faithful of the Church, as it is hierarchically constituted, in which Christ exercises his influence as Head. Reflecting theologically, one discovers that Saint Bonaventure identifies the Eucharist as the sacrament of unity and peace. The solid link that Bonaventure maintains between the Church and the Eucharist, a theme abandoned for centuries by Theology, was rediscovered by the Second Vatican Council and developed by significant 20th century theologies.