Musar sur Le Lévitique 3:16

Even though generosity is a good quality, a person should be careful not to be a spendthrift in order to attain the desires of his heart, in all manner of food and drink or to give of his wealth to harlots, or to have expensive garments made, or to scatter his money in all sorts of schemes that do not lead to reverence of Heaven. A man who is generous should not scatter his funds for nothing or pursue desires which can only bring him all sorts of evil. But he should be very careful to be liberal with the deserving poor, to dress them, to feed them with the best, as it is written, "All the fat is the Lord's" (Lev. 3:16). His reward shall be that which is good and treasured, which "Neither hath the eye seen, save God, who worketh for him that waiteth for Him" (Is. 64:3).

The Torah next addresses itself to the sanctification of one's money, one's possessions. We know that there are people who treasure their possessions more than they treasure their lives. The Torah wishes to teach such people a moral lesson when it demands that after having invested time and labor in producing a crop, they must allocate part of this crop to people who have neither invested time nor effort in producing it. Starting in 19,9 we have a whole string of such commandments. The Torah commences addressing a multitude, i.e. ובקצרכם את קציר ארצכם, "when you (pl) reap the harvest of your land," only, to switch immediately to the singular in the very same verse, i.e. לא תכלה פאת שדך לקצר, "do not reap all the way." This is the way of the Torah telling the farmer that the פאה, edge of the field that he must leave unharvested, never belonged to him in the first place, but always belonged to the poor by right. The same applies to לקט, the gleanings. Were this not the case, the Torah would have included these items under the heading of the מתנות, gifts, which the farmer has to give away. It would have been be quite inconceivable if the Torah had legislated that such "gifts" should constitute the most inferior produce such as the unripe grapes or prematurely fallen fruit mentioned in verse 10. Someone giving charity is certainly expected to give of the superior part of his produce. The Torah has already taught us that the gifts given to G–d must be the best of the type of animal one has offered as a sacrifice, i.e. כי חלב לה' (Leviticus 3,16).