Rashi states: “’You shall leave.’ Leave it before them and let them gather it up. And you shall not help one of them. ‘I am Hashem, your G-d.’ Who is faithful to give reward.”
Sefer Otzros Hatorah asks why the owner of the field is told not to help the poor man. If he wants to make things easier by helping his downtrodden brother, why isn’t he allowed to do that mitzvah?
He answers that the Torah recognizes that if the owner would assist the poor man, he would feel, to some extent, that it is his field and he is being kind to the pauper by giving him charity. He would feel a bit haughty, as if he were the giver and the poor man is the taker. This also might cause the pauper to feel some embarrassment.
Therefore, the owner is told to simply abandon the peah and leave them for the poor man to take on his own, as this clearly shows that his field does not really belong to him. Rather, it belongs to Hashem, and He provides both for the owner and the poor man.
