Vocabulary
A vocabulary is a collection of words.  As a writer, the more words you have at your command, the better able you are to express ideas and feelings—to communicate with others.  Nearly all cultures have praised those of its members who were good with words.  Odysseus, for example, was feared by the Trojans because of his wit and facility with words.  The Anglo-Saxons praised those who had a great “word hoard” and honored those accomplished in speaking.  Even today people who are skillful at communicating in speech and in writing are promoted and paid more than others who are not.  A television advertisement selling a vocabulary-building course says, rather ominously, that “you are judged by the words you use.”
Words—their use and misuse—are very important because they define our conceptual world.  As a linguistic philosopher once said, “The limits of my language are the limits of my world.”