How important is it for a TEFL teacher to know a lot about the English language?

Without proper knowledge a TEFL teacher will neither teach properly nor can she solve the problems of the students. Hence it is necessary to have a lot of knowledge about the subject.

It is obligatory otherwise they won't be persuasive.the most important is that teachers feel modest to get information as it is one of the qualities of knowledge seekers.the other quality is to respect the giver and to be good listeners.