Musar zu Wajikra 23:22

לא תכלה פאת שדך . The reason for the demand to leave a corner of one's field unharvested and to leave other parts of the harvest for the poor, (19,9) has to do with the poor man's quarreling with Heavenly Justice complaining about his underprivileged status. The four kinds of harvest left-overs designated by the Torah for the poor are designed to restore peace and harmony between the poor and G–d. They are able to do this because they apply to bread and wine, the two major components in man's eating habits. The poor derives some satisfaction when he observes that at the very time when the landowner has reason to be most smug and self-satisfied, i.e. when he brings in his harvest, he is reminded by this legislation that he himself is subservient to a Higher Authority, i.e. to G–d.