Jamieson, Fausset and Brown on Leviticus 19:9-10

9-10. And when ye reap the harvest of your land, thou shalt not wholly reap the corners of thy field--The right of the poor in Israel to glean after reapers, as well as to the unreaped corners of the field, was secured by a positive statute; and this, in addition to other enactments connected with the ceremonial law, formed a beneficial provision for their support. At the same time, proprietors were not obliged to admit them into the field until the grain had been carried off the field; and they seem also to have been left at liberty to choose the poor whom they deemed the most deserving or needful (Ru 2:2, 8). This was the earliest law for the benefit of the poor that we read of in the code of any people; and it combined in admirable union the obligation of a public duty with the exercise of private and voluntary benevolence at a time when the hearts of the rich would be strongly inclined to liberality.