Most professional job applications include a cover letter in addition to a resume and reference sheet.

Cover letters provide job applicants with the opportunity to:

• Introduce themself - in a more narrative and nuanced way than is possible in a resume
• Highlight their most relevant and impressive qualifications
• Make it clear what they have to offer the employer and those they serve
• Proactively address resume information gaps - if deemed necessary
• Express enthusiasm and interest in a position and/or business/organization
• Inspire employers to invite you to an interview

Emphasize what you can do for the employer (vs. the other way around), and answer the following questions for them:

• Does this applicant really want this job - ie. for the right reasons?
• Will this applicant be better at this job than other applicants?
• Could this applicant be a great fit for this business/organization?
• Would it be worthwhile to interview this applicant?

A cover letter can also serve as a useful interview prep aid,  since it will include professional language to describe the most exemplary and relevant qualifications for a particular position.