*Is it to burn fat?
*Is it to gain muscle?
*Is it to feel better?
*Is it to look better?
*Is it to fit in a dress you've always wanted?
*Is it to fit in a dress you used to wear?
*Is it to be part of a community?
*Is it a hobby?
*Is it your idea of play? 
*Are you just looking for a new playground? 
*Is it a sport you like?
*Is it something you can get better at with time?
*Is it to improve quality of life?
*Is it to ensure quality of life?
*Is it to improve longevity?
*Is it the first thing you look forward to doing in the morning?
*Is it the thing you look forward to after a long day?
*Is it to get more done in an hour?
*Is it to be able to do more in an hour?
*Is it to reduce the odds of being knocked down by a lifestyle disease?
*Is it to better manage a lifestyle disease?
*Is it to keep aches and pains away?
*Is it to manage aches and pains?
*Is it to to improve your performance at another activity?
*Is it to be able to hop across a puddle? 
*Is it to give your day more structure?
*Is it to inspire someone around you?
*Is it to motivate someone around you to take the first step?
*Is it the lack of a better idea?
*Is it your best idea?
*Is it the sense of achievement?
*Is it the sense of purpose while you do it?

Maybe it just leaves you feeling better than ever

That long list is just the tip of the iceberg in the list of reasons to get a consistent dose of activity. There are more personal reasons to do this. That you start moving today is all that matters.