Last week (Parshat Mishpatim) someone turned to me and shared his vague recollection of a vort of the Baal Shem Tov. The Dvar Torah (as clarified vis Googling, and finding this site) goes something like this:
"If you see the donkey (chamor) of your adversary collapsing under its burden, and you hesitate to assist him, you must surely assist him."
The body is material substance (chomer). The body is attracted to material matters, while the soul is attracted to spiritual matters. G-d created the body out of material substance with the intention that the physical matter be made into a receptacle for G-dliness. This is the "burden" that the body bears.
When you see the body collapsing under his burden you may "hesitate to assist him" - you may refrain from assisting the chomer in carrying out the Divine plan. The body is chomer and has no choice but to eat, sleep, etc; but all this must be done as an avodah. When you see the chomer "collapsing under its burden," you may be unwilling to assist it and choose instead to undertake a program of fasting and self-mortification in an attempt to break the chomer. The Torah way forbids breaking one’s body through fasting and self-mortification, and instead requires that "you must surely assist him" - you must allow the chomer to remain with the body, and work toward holiness jointly with body and soul.