It is imperative for a language teacher to have a good grounding in linguistics because linguistics is the scientific study of language in terms of

• a) how it is learned
• b) how it is applied academically and socially
• c) its relationship to cultural behaviors 
• d) its connection to literacy 
• e) its nonverbal system of communication

There is a lot much more that is covered in the field of linguistics, but notice how important it is to be content-grounded in order to be able to teach the ways in which language can be used and applied. From the study of linguistics, other sub-fields branch out to include

• a: Applied Linguistics- explains the way in which language operates with an academic, technological, social, ethnic, and scientific setting.
• b: Ethnolinguistics and dialectology- explain the language/culture connection as well as the variation in language usage among different cultures.

The branches above reflect the importance of being well-educated in linguistics from a cultural and social focus. Now, look at the other branches of linguistics which are even more specialized and are equally important to be mastered.

• c) Morphology- teaches about word formation and inflection.
• d) Syntax- is the study of sentence structures
• e) Semantics- explore the meanings of words and of sentences.
• f) Phonetics- explains how words should sound and how they should be articulated.

Imagine a teacher attempting to teach a language system without any knowledge of how its words are formed, pronounced, and properly used? Contrastingly, picture a teacher who has tremendous command of the language, and of its linguistic components in academics and society: the teaching will be more effective because the teacher will have more well-known resources to pull from. Also, a teacher with a strong knowledge of linguistics will be able to problem-solve the common miscues that occur through the process of second language learning. In all, a knowledge of linguistics is essential for a language teacher to provide quality teaching.