"Know Him in all your ways" says King Solomon in the book of Proverbs; "All
your deeds should be for the sake of Heaven" quotes Ethics of the Fathers.
The Jew serves G-d not only with Torah study, prayer and the observance of
the mitzvot, but also with his or her every act, including the seemingly mundane
act of eating.
There are times when the act of eating is itself a mitzvah -- eating
matzah on Passover, for example. But also when this is not the case, the Jew
does not simply eat; he or she eats "for the sake of Heaven" -- with the
intent to utilize the energy derived from the food to serve G-d. The Kabbalists
teach that when we eat with such mindfulness we "elevate" the food, redeeming
the "spark of G-dliness" it contains by fulfilling the purpose to which it was
created.