The purpose of language is communication- not communication in a void, but communication between the writers or speakers and their audiences. Communication styles of writers and speakers will reflect their personalities and backgrounds. However, the way they express themselves should be consistent with the nature and background of their audiences.
The main idea of this paragraph is that
a) the language people use reflects their backgrounds and natures.
b) how people speak must reflect their audiences' backgrounds and natures
c) communication does not take place in a void, but between people
d) to communicate effectively, people should consider their audiences while being themselves