The Zohar, Chapter “Miketz (At the End),” Item 117: When a person rises in the morning, he should wash his hands from a Natlah of water, which is a vessel from which to take water [a special cup for ritual hand-washing].
“Morning” means that the Light of Hassadim comes and the illumination of Hochma is revealed. A person feels the spiritual quality of giving and love as darkness inside of his egoistic (receiving) desires. By correcting them, he awakens for morning and experiences the dawn, and then the day. Inside of his corrected desires he feels the Light of Bestowal.
All of this occurs inside the same desires. At first a person feels that the spiritual world is darkness – something that is repulsive and undesired because it is related to bestowal and the need to love the neighbor. He then goes through correction by studying during the nights (and according to the connection of “branch and root,” we also study at night). Thus, he prepares for the coming of day; he reaches the understanding that spirituality, bestowal, and love for one’s neighbor is day – that it is good, and therefore, he desires it.
Because of his intention, the Surrounding Light gradually begins to influence him, making the state that seemed like darkness to him before look desirable. The same state turns into day and begins to shine.
These corrections that a person performs to his desires are called “hand-washing,” since “hands” are the receiving desires, which need to be cleansed of egoistic intentions before they can be used. The “special cup for ritual hand-washing,” the Upper Vessel, Bina, pours the Light of Correction upon our receiving desires.