Deuteronomy 24:20, commentary and pictures

When the olive tree is beaten at harvest, its boughs are not to be gone over a second time, but what remains is to be left for the stranger, for the fatherless, and for the widow.
The leftover olives after the first beating belong to the vulnerable by right, and owners are forbidden to collect every last olive for their own advantage.
Practical care for needy people is thus made a duty, and the law stands as a protection of the poor against oppression.

The olive command belongs to a wider harvest provision that also forbids reaping wholly the corners of the field, going back for a forgotten sheaf, and gleaning the vineyard afterward, so that grain, olives, and grapes are always reserved for the poor.
The same provision allows the hungry to eat grain or fruit while passing through a neighbor's field, as illustrated when the disciples ate grain passing through a field.
The command teaches practical provision and consideration for people in need, with mercy, compassion, and generosity expressing the same principles later taught by Christ.
Generosity toward people in need is joined with gratitude for God's mercy and remembrance of Israel's former bondage in Egypt.
It belongs to a divine rule of strict integrity that puts aside all desire for selfish gain, with the promise that the Lord will bless all the work of the hands.

The rule reveals God's benevolence in making ample provision for the wants of all mankind, entrusting His goods to representatives to supply the needs of all His creatures.
He never meant for misery to exist or for one to have abundance of luxuries while others cry for bread, so that temporal as well as spiritual blessings are for all.
It educated Israel that while standing distinct and holy and separate from nations that did not know God, they were to treat the stranger kindly, not despise him for not being of Israel but love him.
The stranger was to be made welcome at feasts of thanksgiving when recounting God's mercies, and to be received into fellowship to learn God's law and glorify Him by obedience if he chose the society of those who acknowledged God, so strangers shared in both material provision and spiritual blessings.

For Christians the command requires integrity that realizes God's eye is upon them in buying and selling, being just what they profess to be, guided by truth and uprightness.
It forbids scheming, false balances and deceitful weights, oppression of hired servants, perversion of justice, keeping back wages, and enlarging possessions by taking advantage of a neighbor.
It requires accepting only a fair price, frankly disclosing defects even at cost to self, and relieving the necessities of a less fortunate brother.
Israel had received special instruction in this sharing with those in need but failed to extend help to suffering people.