During the Middle Ages, almost all philosophers used to write in Latin- the language of educated and elite class while as Dante wrote his best poem Divine Comedy in vernacular, Italian language-the language of common people.
Dante's decision to write in Italian had a long lasting impact on Italian language. It paved the way for Italian to emerge as a language respect across the European landscape. There were more innovations in this language and more and more people began to write in Italian and ultimately Italian became a cultured and literary language. It is due to the impact of his writing in Italian, he is being called father of modern Italian language.