When you read a work of literature written during a particular period of history, one of your main concerns should be to determine its usefulness as a historical document. Law codes, to take an easy example, can tell you much about the social and economic conditions of the people who passed these laws, as well as revealing what kinds of crimes their society was most likely to experience. Personal letters can give you a sense of being on the spot as events took place.
Epic poems reveal heroic values.
Satires and comedies point up the current foibles of society. Religious books are usually sincere expressions of faith, and philosophical writings express the highest levels of intellectual life. Try to determine when, where, and why this book was written. Remember that a book about the Hundred Years' War written by an English archer will have a different slant than one written by a French knight. You must, however, be alert to obvious one-sided arguments.