Although your résumé is definitely important, the cover letter can also be a make-or-break factor. Before you even get an interview, your application will have to impress the recruiter or hiring manager, so perfecting your cover letter is key to earning a face-to-face meet.
Think no one reads a cover letter? WRONG! The small things really do make the difference. Some hiring managers only look at a cover letter because it should give them everything they really want to know about you. http://www.classycareergirl.com/2013/03/the-13-best-kept-cover-letter-secrets/