The Canterbury Tales by Geoffrey Chaucer are still important for several reasons. First, they are really good stories. They also, in the way they show the pilgrims coping with the results of the black plague, suggest ways we can respond to great tragedies such as plagues and natural disasters.
Next, they mark an important phase in the history of English literature. Perhaps the single most significant historical event for English literature was the Norman Conquest of 1066. Before that, the English spoke Anglo-Saxon or Old English and wrote poems like Beowulf in strong stress meter. The Normans brought to England the French language that merged with Old English to form Middle English. Norman verse was written in syllabic as opposed to strong stress meter. In Chaucer, we see the development of accentual syllabic meter in the form of iambic pentameter and the evolution of many of the stylistic features that would come to dominate modern English verse.