Admissions to the graduate/professional school of your choice depends on your application (including references, test scores, essay, etc.) and possibly a campus interview. Admissions committees not only look for people who have the ability to complete the academic work, but hope to find candidates who are thoughtful, mature, articulate, and well-prepared. They will determine whether you possess these attributes by readings your references and essay.
Plan to submit one more reference than the program requested.
(as paraphrased from Asher's Graduate Admissions Essays -- What Works, What Doesn't and Why)
For more detail on writing your essay, and examples of strong essays, stop by my office in the upstairs of Edwards House to review Graduate Admissions Essays -- What Works, What Doesn't and Why by Donald Asher.