Although professors in a university are basically teachers who do the most important thing--- teaching we cannot ignore one more influential aspect that they are always busy with--- doing research
I dont understand why you leave --- !
It's better you say this idea in a more effective way;
Although the main responsiblity of professors is to teach, it is also important that they engage in research studies .In my opinion, a professor should spend more time doing research rather than educating students for athe following few reasons following .
A professor means a researcher or an expert of a specific science subject
.... it is not fair to specify a particular discipline of studies. Professor can be a specialist in commerce, economics, music, history etc.
He or she should always keep the passion in her field so that he or she could push him/herself forward all the time.
------------ actually you are going a little out of topic... this essay is about whether a prof should teach or do research.... so, you don't have to talk about how passionately they need to involove with their work.