Henri de Lubac's Corpus Mysticum, published during and immediately after the conditions of wartime France, had a profound influence on the theology and actual practice of not only Catholic, but also much Protestant liturgy in the course of the unfolding liturgical movement. The interpretative keys of the text were established primarily by Michel de Certeau and Hans Urs von Balthasar, and have emphasised a historical shift from understanding in the connections between a threefold hermeneutic of Christ's ‘mystical body’. The ‘mystical body’ is variously understood as the Eucharist itself, the extant body of the Church, and the actual body of Christ. The conventional reading of this text is to claim that de Lubac traces a shift, occurring in the High Middle Ages that points away from the body of the Church to an objectification of the eucharistic species, resulting in the highly individualistic piety that manifested itself in the Catholicism of the nineteenth century. This paper challenges that hermeneutic key as an oversimplification of a much more subtle reading suggested by de Lubac himself and intrinsic to the text of Corpus Mysticum, and suggests that de Lubac understood the real shift to be the triumph of a certain kind of rationalism, exemplified by Berengar's thought, emerging to assert itself as the basis and ground of theological thinking, eclipsing the grounding character of the liturgy as the source of meaning in theology. It examines de Lubac's late claim that Corpus Mysticum was ‘a naïve text’ and asks what kinds of naïvety are indicated in this statement.