John Gill Commentary Deuteronomy 24:20

"When thou beatest thine olive-tree, thou shalt not go over the boughs again: it shall be for the sojourner, for the fatherless, and for the widow." — Deuteronomy 24:20 (ASV)

When you beat your olive tree
With sticks and staves, to get off the olives when ripe.

you shall not go over the boughs again;
to beat off some few that may remain; they were not nicely to examine the boughs over again, whether there were any left or not.

it shall be for the stranger, for the fatherless, and for the widow;
who might come into their oliveyards after the trees had been beaten, and gather what were left.