What are the purposes for which we use languages in the classroom?

Well the classroom resembles real life, it's like a small society, where a teacher and students have shared benefits that they take from one another, in other words they communicate, and that's why they use languages.
now if you're a language teacher it's think its a great idea to communicate your questions or demands to the students in the language you're teaching, this will help student actually use the language to think and produce responses to the teacher's demands.

We use language to communicate and that's what differentiate us from animals.
And of course...since the world has been made very well, body language exists too for the ones that can't talk.
This also differentiate us from animals.