Why are you interested in this job?
Because it offers everything I've been looking for, both in the position and in the overall environment. It fits perfectly with my career plans.
Everything I've accomplished in my career to date has prepared me to perform the job you need done. My background in _______________________, my experience with ____________________, and my training in _______________________ uniquely qualify me to perform this job better than anyone else.
You won't find a better candidate or a more dedicated employee.