When a person performs a mitzva, he attains, on the highest level that he can, unity with the divine light.
Each mitzva is a kind of window, a particular point of view regarding the Divine.
The person who performs the mitzva binds himself in this way to the divine essence.
In this sense, the tefillin and Torah embody this connection only while the person is performing the mitzva.
In order for the union between the human “l” and the supernal will to be formed, a person needs to complete the circuit.
This is analogous to the spinal cord.
The spinal cord passes through the vertebrae to make a living connection between the upper part of the human organism and its other parts.
The spinal cord cannot exist without the vertebrae, and if one of the vertebrae breaks or even moves slightly, the whole structure may be damaged.
In the same way, the object comprising a mitzva, such as tzitzit, Sabbath candles, or the letters that make up the Torah and prayers, corresponds to the vertebrae.
All that the person does is connect the vertebrae-like conduits, or electrical wires, to connect the current between the upper part, which is the infinite light, and the lower part, which is the divine soul in the human body.
This idea is found in a verse: “Before the silver cord is severed” (Eccles. 12:6).
The cord of silver, kesef, is the cord of yearning, kisufim, between the upper and the lower, the source of life above, and the place where the soul has been embedded below.
Through this silver cord, the yearning soul is connected to the Creator with the infinite light.
The soul on one end and the divine light on the other join together in the mitzva, or in the words of Torah or prayer, and thus they establish the “silver” (yearning) connection.
Rabbi Adin Steinsaltz