The interview is very important for medical school. In fact, the interview is the very reason why a lot of qualified applicants (on paper) do not get accepted into medical school. To put it simply, this is how medical schools generally work.
Medical schools consider GPA, MCAT, letters of recommendations, personal statements, extracurricular activities, etc to determine whether an applicant is invited to an interview. It is hard to get to get an interview at medical schools. If you get an interview at a medical school, you are more than half way there to getting accepted. Medical schools only accept a small percentage of students for the interview process.
Everyone who gets invited for an interview is considered a qualified applicant by that particular medical school. Generally, everyone is now in the same boat. Now your performance on the interview is generally more important than how you “look on paper.” Unfortunately, if you are horrible at interviews, it will be hard for you to get accepted into medical school even if you have perfect scores. It makes sense though since you need to be able articulate things to patients as a doctor.
Do not underestimate the importance of an interview. If your college offers mock interviews, make sure to take advantage of them.