One of the lesser known laws mentioned in פרשת כי תבוא is והלכת בדרכיו, that we are to walk in Hashem's ways. The Rambam uses this Mitzva as the basis for staying physically fit. He says that we are to walk in Hashem's ways and not crawl in his ways.
This is the basis for הלכות דעות, the laws of dispositions in the Mishna Torah of the Rambam. We are to eat right and exercise so that we are able to literally walk and not crawl in Hashem's ways.
The של״ה הקודש adds a little to the previous idea. He says that not only must we try to see to it that all of our limbs are in perfect condition, but this also applies to our spiritual and emotional faculties. They, too, must be in good working order.
We must be gracious to others, as G-d is gracious to us. When we fulfill והלכת בדרכיו, we become a מרכבה, a carrier of Hashem's Presence on earth. Man's purpose is to perfect his resemblance to the Divine. We do this by fulfilling, והלכת בדרכיו. Shabbat Shalom