First, forget about the film. If you really want to watch Christian Slater's porn debut, at least read the book first.
What is this book about?
The story follows William of Baskerville, modeled after Sherlock Holmes, attempting to resolve suspicious deaths in a 14th century Italian monastery and debating with a Papal legate over the disputes between the Catholic Church and the Emperor. The tale is narrated by William's novice monk, who is now old and remembering the events as they took place over the course of one week.
This book should be mandatory reading for people interested in grimoires. Many of the basic concepts of grimoire literature are derived from this time of theological instability, when the previously insular Church was exposed to foreign ideas from Jews, Muslims, and other ways of thinking. The story follows some important events in Church politics that led to some forms of esotericism being validated as sacred writings, and others being relegated to Forbidden Dark Secrets. Peter of Abano makes a couple of cameo appearances.
The story addresses modern politics as well. It characterizes the Dulcinian Heresy as a form of Communism, contrasting it to the more democratic Benedictine order and the Imperial fascists. Ultimately people would rather have to live under a flawed democracy, or even a bad king, than succumb to a world of drop outs who end up starving until they become a violent mob. It is possible to read that part of the story as a commentary on the Hippies.
If you did not grow up Catholic or study medieval life and literature, frankly, a lot of this book will make no sense. Consider that a chance to learn a bit of Latin. The author died a couple of years ago, and all of his works are worth reading, but I expect that students of ideas from that period (14th Century Europe) will benefit much more from them than the average reader.