A Muslim teacher is first a Muslim and then a teacher.  A great deal of responsibilities lie upon the shoulder of a Muslim teacher. 

Allaah (ta'aalaa) says:  Truely the one who fears Allaah is the scholar.  Indeed, a Muslim teacher should have fear of Allaah in his heart in order to have a good start in this career.  This fear will teach him to have the other qualities necessary to make him excell in this career as he does all this for the sake of Allaah.