An introduction about the teachers' views about the role and nature of EnglishSociolinguistics
The English language surfaced as the social communication between Germanic invading tribes that spread about the land, combined with Anglo Norman and West Saxon. It would take chapters to extend this answer, but it is the most concise as far as the origins of the language itself.
As far as the acquisition of its own unique language and vocabulary, it all began when the court, which was in Westminster, carried on its daily activities in London. London was a magestically huge port in which you can trace the first signs of a medieval, cosmopolitan metropolis. Everyone from vendors to artists, gypsies, workers, courtiers, slaves, servants, tradesmen from all over Britain and the nearby countries came to London to seek the opportunities that come from a city that has direct contact with the sea and which has a booming economy.
London, itself, from medieval times was a world of its own, and its sociology was completely different from that of the rest of England. The combination of integrative lexicon, the influence of multiculturalism, the constant exposure to diverse languages, and the social need to establish a set vocabulary to conduct trade is ultimately what became the English that continues to develop to this day.
As far as its role, I was taught as an ESL student that the role of the English language is to make language universal. It is a unifying language whose history is as interesting as its learning process. Not that it will be eternally the world's global language, but certainly will be for a while until people decide otherwise.