An impressive resume and cover letter will get you an interview.
A successful interview, followed by a thank you letter that reiterates your suitability for the position, will get your name on the shortlist of people to be considered for the job.
But it is the excellent reference that will cinch the deal!
If a reference letter is requested, it must address the skills or attributes that will enable you to succeed in the role you are applying for. It must be a distinct reference letter that addresses your suitability for that particular job application. Most Recruiters report that they do not read cover letters, but hiring managers do read them!
A well-written reference letter highlighting your suitability for the position and repeating a few essential facts from your resume will be a valuable addition to your application package.
Have your reference letters prepared in advance and remember to take them to the interview take to the interview.