All good teachers ought to have a passion not only for what they are teaching, but also for who they are teaching.  Passion is a motivating factor for the one who possesses it, but it is also a contagious source of momentum for those who are exposed to it.  Is teaching possible without passion?  Yes.  Is it enjoyable? No.  Neither student nor teacher will enjoy their experience if the teacher lacks passion for either their audience or their material.

I could never, ever teach a math class.  There is absolutely no passion in any fiber of my being towards math.  Languages, on the other hand, fascinate me.  I love to explore different languages and the different ways people communicate.  Even when I was faced with teaching languages I didn't know, I enjoyed the experience.  (Not sure the students learned so much, since I was learning for the first time, too.)  I am passionate about languages.  Folks who are passionate about their subject often burn out or "bore" out.  

While I happen to enjoy most stages and ages of life, I am not passionate about the middle school age group.  I would prefer to work with high school aged students.  Teachers who love middle school aged students, love teaching middle school aged students.  They enjoy all the things that come with that territory while others would rather poke their eyes out.  You need to be passionate about the type of audience that will be staring you in the face day after day.

Passion is an essential quality for a good teacher to possess.