John Calvin Commentary Deuteronomy 24:19

"When thou reapest thy harvest in thy field, and hast forgot a sheaf in the field, thou shalt not go again to fetch it: it shall be for the sojourner, for the fatherless, and for the widow; that Jehovah thy God may bless thee in all the work of thy hands." — Deuteronomy 24:19 (ASV)

God here impresses upon landowners the importance of liberality when their fruits are gathered. For when His bounty is displayed before our eyes, it invites us to imitate Him; and it is a sign of ingratitude to unkindly and maliciously withhold what we receive from His blessing.

Indeed, God does not require that those who have abundance should give away their produce so lavishly as to impoverish themselves by enriching others. In fact, Paul prescribes this as the measure of our alms: that their relief for the poor should not cause distress to the rich themselves, who kindly distribute (2 Corinthians 8:13).

God, therefore, permits everyone to reap their grain, gather their vintage, and enjoy their abundance, provided that the rich, content with their own vintage and harvest, do not begrudge the poor the gleanings of the grapes and grain.

This does not mean that He absolutely assigns to the poor whatever remains, so that they may seize it as their own; but rather that some small portion may flow freely to them from the generosity of the rich.

He indeed mentions by name the orphans, widows, and strangers, yet He undoubtedly designates all the poor and needy who have no fields of their own to sow or reap. For it will sometimes occur that orphans are by no means in need, but instead have the means to be generous themselves; nor are widows and strangers always hungry. But I have explained elsewhere why these three groups are mentioned.