Well, my essay began with a discussion of why I turned down Georgetown for undergrad (b/c I might not have been able to complete my premed requirements as a student of the School of Languages and Linguistics), and why I had a hard time making the decision -- because I liked the school so much when I visited (location, great reputation, friendly students).
I'm not religious but think all students can benefit from learning about the spiritual/ethical aspects of medicine, so I wrote about that along with the other typical stuff I write in all "why do you want to go to our school" essays.