Just as with the mitzva of tefillin, for example, there is a designated place for them on the head and arm, and one feels the weight of the head-tefilla and the tightness of the hand-tefilla, so too with the mitzvot of love and fear of G-d... the fulfillment of these mitzvot is that there be a bodily sensation, that the very flesh of the heart actually feel; just as, for example, [the love one feels] when one meets a truly devoted friend.