The rest of the admissions packet contains sterile transcripts, lists of activities, test scores and so on. The essay is your one chance to demonstrate your uniqueness. What you write is critically important as it shows your mastery of thinking, analyzing and addressing the issue. How you present the content is equally important as it tells them something about what's important to you, your personality, the way you think, etc. Admissions readers need to gain some sense of who you are, both as a student and person, through your essay.
Essays are the one part of the application package that tend to delay the entire process.
Pick a time and place that is free from distractions and conducive to writing. If you need some help getting started, pick someone who knows you well and can help 'brainstorm' some ideas that highlight your individuality. If you have a choice of essay topics, decide which ones you're comfortable with and which ones will provide the opportunity to tell 'your story'. Stick with more personal ideas that reflect something about you. After reading your essay, admissions officers should have an emotional reaction about YOU, not an intellectual reaction about your essay topic.