The mitzvah of charity and loving-kindness is an expression or irradiation of the Sefirah of Chesed, bringing Divine Light down into the world.
When one fulfills this mitzvah of charity, the hand that offers the free gift is the hand of God.
It is God who is bringing down loving-kindness through the agency of the human hand.
Just as, in our daily prayers, we repeat the supplication phrase to God, "who brings down the rain," and at the same time, realize that it is not a miraculous intervention in nature but that clouds and wind and temperature are conjoined to act as agents for the blessed downpour.
In this sense, incidentally, Divine chesed is often depicted as rain, with a particular person–like a wind-borne cloud–acting as His instrument.
The element of self-nullification is here very important, because the act of giving charity is valid only when a person is connected to a source (when he does not feel himself as the doer), when he feels that his hand is an implement of a Divine wish, and he himself is in some way or other eliminated.
He has become an indirect instrument of something else and has somehow been separated from the act.
The hand that gives charity is not his.
–Rabbi Adin Steinsaltz
From "Sanctity and Restraint" in The Candle of God by Rabbi Adin Steinsaltz