Letter of interest?

Hey guys! I would like to get some feedback on this. There is a job posting for a mental health tech near me. I have been looking for such a position for a couple months because I would really like to work mental health when I get my rn. However, looking at my resume, I just don't know if it will be strong enough to make me a consideration. All of my experience is in retail/customer service. Would it be better to submit a letter of interest to the hospital letting them know why I am interested, and how I feel this position will help me realize my future career goals?
Send a letter of interest along with your resume...make sure your letter gives the full picture of your interest.