As society grows and changes, so does the literature. If society is very religious or dealing with severe uprisings, the literature written during that time will also reflect these things since the authors will be likely dealing with or at least aware of societal norms for that specific time. This is also true for French literature.
These societal and literary changes are usually grouped by century or period such as the 16th century or the medieval period. Many pieces of literature written during the medieval period had to do with religious themes and were written in Old French, rather that the contemporary French used today.