This page organizes vocabulary lists based on works of literature.
Concordances have their own namespace "Concordance:".
Rationale for having concordances: Someone reading the stories of Sherlock Holmes, for example, may need to look up rare and obsolete words even if they are a native speaker; someone reading Shakespeare certainly would! Someone reading the works of Doctor Seuss as an aid to learning English (or just pronunciation of English) may find it handy to have a vocabulary list. This is very important for languages like Farsi (Persian) which have a high degree of diglossia.