I would say that it’s not *that* important. It’s one of the many data points used to assess your chances for admission. 

• The general GRE is not very useful in evaluating the potential for graduate school.  
• The problem is that students from different majors take it and do just fine depending on their undergraduate courses.  
• There are also a lot of test prep materials available and even classes that can help with the GRE.
• A student should have a decent understanding of algebra, geometry, logic, and statistics before going to graduate school.  
• Having a good score on the GRE doesn’t tell you much about their ability to do research.