The mitzva of charity is to give of oneself to another.
The giving of money in an act of charity does not fully encapsulate the depths of this mitzva, which in truth extends far beyond what can be discerned by this isolated act.
The act of giving can be viewed as a summation of the broad scope of efforts and actions the vital soul expended and executed over the course of time, leading up to and culminating in this single act.
The charity money not only expresses the intense labor expended by the vital soul, but also epitomizes its desires and passionate pursuit of wealth – all of which are now condensed within the money being given.
In this sense, the money is invested with the energy, labor, time, and essence of the soul.
When a person then gives this money to charity, he essentially is giving the value of all the energy spent in its acquisition.
The more a person labored and invested in obtaining this money, the more he gives of his soul.
Rabbi Adin Steinsaltz