In the 21th century, books appear in multiform devices without any fixed shape or materiality. The new, virtual concept of the book in the Digital Age makes us realize that the book as a medium has its own history, apart from that of the texts it contained. The paper focusses on the symbolic power assigned to books in Christian liturgy, and on the configuration of their lavishly decorated envelope, the treasure binding. It will be argued that the power of the book depended on materials and images that enfolded it. Only a codex decorated with precious and elaborate “robes” could fully embody the Logos during the ritual. With its tension between excessive materiality and transcendence, the medieval practice of ornating the book hints at a deep polarity between the processes of excarnation and inlibration of the divine. Applying the anthropological notion of “clothing”, the lecture wants to reassess the role of medieval book covers and treasure bindings in the history of media and religion.