(יט) כִּ֣י תִקְצֹר֩ קְצִֽירְךָ֨ בְשָׂדֶ֜ךָ וְשָֽׁכַחְתָּ֧ עֹ֣מֶר בַּשָּׂדֶ֗ה לֹ֤א תָשׁוּב֙ לְקַחְתּ֔וֹ לַגֵּ֛ר לַיָּת֥וֹם וְלָאַלְמָנָ֖ה יִהְיֶ֑ה לְמַ֤עַן יְבָרֶכְךָ֙ יהוה אֱלֹהֶ֔יךָ בְּכֹ֖ל מַעֲשֵׂ֥ה יָדֶֽיךָ׃ {ס} (כ) כִּ֤י תַחְבֹּט֙ זֵֽיתְךָ֔ לֹ֥א תְפַאֵ֖ר אַחֲרֶ֑יךָ לַגֵּ֛ר לַיָּת֥וֹם וְלָאַלְמָנָ֖ה יִהְיֶֽה׃ (כא) כִּ֤י תִבְצֹר֙ כַּרְמְךָ֔ לֹ֥א תְעוֹלֵ֖ל אַחֲרֶ֑יךָ לַגֵּ֛ר לַיָּת֥וֹם וְלָאַלְמָנָ֖ה יִהְיֶֽה׃ (כב) וְזָ֣כַרְתָּ֔ כִּי־עֶ֥בֶד הָיִ֖יתָ בְּאֶ֣רֶץ מִצְרָ֑יִם עַל־כֵּ֞ן אָנֹכִ֤י מְצַוְּךָ֙ לַעֲשׂ֔וֹת אֶת־הַדָּבָ֖ר הַזֶּֽה׃ {ס}
(19) When you reap the harvest in your field and overlook a sheaf in the field, do not turn back to get it; it shall go to the stranger, the fatherless, and the widow—in order that your God יהוה may bless you in all your undertakings. (20) When you beat down the fruit of your olive trees, do not go over them again; that shall go to the stranger, the fatherless, and the widow. (21) When you gather the grapes of your vineyard, do not pick it over again; that shall go to the stranger, the fatherless, and the widow. (22) Always remember that you were a slave in the land of Egypt; therefore do I enjoin you to observe this commandment.
What do we learn from this?
...The commandment to leave over small portions of the grape and olives that you harvest, and not to pick up sheaves that are dropped, yield only miniscule donations.
On the other hand, they drive home a powerful message of the need to limit our ownership for the benefits of the underprivileged other. In that way, they engender a mindset not of charity, the loving benevolent giving of that which is mine, but tzedaka, the socially just redistribution of wealth which comes from accepting the limits of my ownership, from being willing to let go of what I might think of as "mine".
If this letting go is hard, we are to remember how God let us go from Egypt. As representative of the poor, the orphan, the widow, God now asks us to return the favor....
But what the Torah teaches us in chapter 24 is that in some circumstances, dignity, and perhaps even love, supersede any other claims, and require letting go.
(Rabbi Avidan Freedman, https://www.929.org.il/lang/en/page/177/post/51504)
How do we help people?
...This commandment, known as shichechah is one of many commandments that require us to leave some produce behind in the fields for the poor to collect. It’s also a highly unusual commandment, because it seems to be a commandment you can only fulfill unintentionally due to the requirement of forgetting.
The purpose of shichechah isn’t just charity. There are other commandments about charity, and easier, more common and consistent ways to give it. The purpose of shichechah is about giving charity in a way that doesn’t create feelings of indebtedness from the recipient: they can feel that they are not taking anything of real worth, and therefore aren’t imposing in any way on the giver.
This effect is very difficult to create intentionally.... That’s why genuine forgetting is so important.... He could... try to leave some behind and make it look accidental, but it would be hard to know if the correct psychological effect happened or not....
(Jamie Weisbach, https://www.929.org.il/lang/en/page/177/post/51463)
What do we take away from this in today's society?
If the reason for the law had a social purpose,... the poor were hardly protected, for they had to depend on the owner's inadvertance....The mitzvah can be carried out only if one is forgetful; hence it does not emanate entirely from free will. Therefore, the true intent of these laws was seen to be the molding of character: people should learn not to want every last piece of produce and profit.
(Plaut Commentary, p1333)