Sforno on Leviticus 19:9/ספורנו על ויקרא י״ט:ט׳

1ובקצרכם...לעני ולגר תעזוב אותם, The Torah now turns to how we can emulate G’d’s attributes in [practice after having accepted that it is our purpose on earth to emulate G’d’s characteristics to the extent that He has revealed them to us. We are to perform acts of charity and righteousness. Part of such acts of charity are the providing for the underprivileged out of the bounty G’d has seen fit to grant us. The specific items known as leket, shikchah, and peyah are examples of such demonstrations of our generosity towards the poor. אני ה' אלוקיכם, this recognition of G’d as our G’d is demonstrated by our meticulously fulfilling these commandments relating to the time when we gather in our harvest. Before we even give tithes of the completed harvest which has been brought into the barn we already allow for the poor to help themselves to what other, gentile farmers, might consider the product of their own hard earned labour.