“Many scholars believe that classical Latin was spoken by almost no one- that it was used exclusively as a literary and scholarly language. Certainly such evidence as we have of everyday writing- graffiti on the walls of Pompeii, for example- suggests that classical Latin was effectively a dead language as far as common discourse was concerned long before Rome fell. And it was that momentous event- the fall of Rome- that helped usher in [English.]”

From The Mother Tongue: English and How It Got That Way by Bill Bryson

Some universities grew out of a fear of travel spawned by the plague- those seeking a higher education no longer wished to journey far, and so local universities were opened. Teachers for these new universities were often brought up from lower schools because they had a working understanding of Latin. Instead of teaching in Latin, these educators used their own language, known as vernacular. The use of different languages ultimately increased the intellectualism of the era after the plague. Those who learned in their native tongues were the beneficiaries of an education they might not have had otherwise. The better educated a society is, the more likely it is to grow culturally. Many historians believe the dual progress of Latin and the vernacular led to the Renaissance.
The Black Death by Stephanie True Peters