I recently came across this piece written by Jim Wofford, an American author and master horseman on the topic of 'self-carriage', which is usually a training ideal discussed within dressage circles:
http://practicalhorsemanmag.com/article/harmony-through-self-carriage-11827
I think that we must be aware of the philosophical benefits of self-carriage as well. It is a complicated, uneasy world that we live in these days, and any small interval of mental and physical balance is a treasure. I think those moments of self-carriage when we ride speak to something deeper than just some technical state of equilibrium.
At its best, our riding centers us above our horses. When we are centered above our horses, we are centered above the earth, and for that moment, however brief, we are centered in the natural world, we are harmonious with it and we are at peace.
Have a very Merry Christmas, and Peace on Earth!