There was very little media in the way we use the term in the Middle Ages. There were some signs (such as on blacksmiths', tailors', and taverns), art (usually in churches), and things like stained-glass windows, but the primary medium of mass communication was books. Obviously there was no electricity and nothing electronic, so there was no television or computers or internet.
A special manuscript (possibly a lost treatise by Aristotle) is held in the monastery -- and the monastery has a copy-room (a Scriptorium). In this copy-room the knowledge of the ancient world (along with sacred texts and current medieval theology and philosophy) is copied by hand into books. This important function saved a great deal of the knowledge learned in the ancient world from destruction during the dark ages. This secret manuscript has poison embedded in its pages -- this is how several of the people in the novel are killed. One of the monks, Jorge, has decided that this manuscript is heretical and dangerous, and he ends up killing himself by eating it.
Almost everyone's motivation in this novel is somehow connected to the main medium of their times -- books.