It makes me a better me.
I've been a runner officially since college although I've alway liked to run because of the achievement I feel during and after.  Although I ran sporadically freshman through junior year of college, it wasn't until senior year that I dedicated a bigger part of my life to running.  I had picked up a book at my local book store about running a marathon.  I made it my goal then and there to run a marathon.  I was religious about sticking to my schedule (which I later learned is not always the best way to be as I injured my knee and overworked myself).  It's been four years since then and I've run one marathon, three half-marathons, a 15K, and a 5K.  
Running has changed my life in countless ways.  It's no longer just about running a marathon, but a lifetime goal to gain endurance and strength.  I'm a better person on the days I get up and run first even if it's just 30 minutes on a treadmill.  I feel better about myself and I can give more to the world around me on those days.  That's not to say rest days aren't incredibly important as well.
My goals now still include many more marathons and other races, but running is a part of me and I want to run for years to come. 
 *Below is a basic half marathon training plan:
If you're new to running, I wouldn't jump right to the half marathon (although I did), but start slowly as needed.  That's the joy of can be a lifetime of continuous goals.
My husband and I got these Nike sneakers on sale at because they were crazy colors that must not have been selling.  Well they were perfect for us on race day!  And they definitely wake me up when I go running in the morning!  Part of the joy of running is splurging on gear.  I like to think that if I've put in the work then I definitely deserve a new running top, new sports bra, socks, or pair of sneakers - I like to reward myself!  It keeps things fun.