Medieval scholars read every text—poetry, Scripture, philosophy—using four interpretive modes: literal, allegorical, moral, and analogical. A great writer like Dante was expected to keep all four modes in mind, to elevate readers mentally, emotionally, morally, and spiritually. In modern times, critics also assume great writers will make their work entertaining.
Umberto Eco is great by both standards. His medieval mystery novel/theological treatise/philosophical essay/semiotic investigation evidences all those elements, infused with a brilliant style that retains its power in translation (Eco writes in Italian). In The Name of the Rose he explores ideas of secular and sacred authority, and the interplay between faith and reason.
Brother William of Baskerville arrives at a Benedictine monastery in northern Italy to investigate claims of heresy leveled against the monks in residence. Seven murders refocus his investigation, and Brother William solves the mystery using Aristotelian logic. Though he employs reason, he's forced by the nature of the crimes and his surroundings to interpret the evidence in terms of their theological and philosophical context, particularly the monks' preoccupation with the Antichrist and the Apocalypse.
Eco conveys the attitudes of the Middle Ages without burdening the narrative with modern commentary. Brother William doubts everything from religion to the nature of reality, but they're Medieval doubts, not 20th century ones imposed on him by an inept author. Eco's first novel is in many ways his greatest masterpiece, and certainly the best introduction to the work of one of the most important Continental writers of the last 50 years.