Why is the Norman Conquest of 1066 so important to us as we read English literature?

Because of the Norman Conquest, the written language, that of the Norman nobles who virtually slaughtered most of the Saxons at the Battle of Hastings, became French.  This Old French was the language of the Arthurian legends (e.g. "La Morte d'Arthur".  But, when Geoffrey Chaucer wrote "The Canterbury Tales" he broke with tradition and wrote in Old English. 

Nevertheless, the sentence structure of Old English is much like French (e.g. of + noun for possessives, adjectives follow nouns )and meanings of many of the words are the French meanings.  If a student has had French, he/she can more easily read this Old English literature.  In fact even in modern English, more than 60% of the words are derived from French.  So, this French influence continues today as French is a parent language of English.