Baal HaSulam, The Study of the Ten Sefirot, Part 1, “Table of Questions and Answers for the Meaning of the Words”: Question 14. What is Hitpashtut (the spreading of the Light).
Ohr (Light) that stems from the Maatzil (the Emanator) to the Ne’etzal (the emanated being) is called Hitpashtut of Ohr. In fact, the Ohr Elyon (the upper Light) is not affected in any way by that. It is like lighting one candle from another, when the first is not lessened by it. The name only indicates the reception of the Ne’etzal.
When the creature suddenly feels this fulfillment in some particular way, it is considered that the Light enters it. The Light “shines” to us in so far as we react to it, to the degree of our ability to sense It. And if we are not capable of this, it is considered that we have no Light, and the Light goes out, departs.
We talk about the Light as if it goes in and out, about Lights that “swing” the vessels, perform some actions. In reality, the Light does not alter its effect on a desire. Desires are organized in such a way that they continually update informational genes (Reshimot) against the background of the constant Light. And therefore, the desire (vessel) reacts differently and feels as if the Light flows through it, changes, excites it, or goes out.
All of that is a consequence of our incorrect perception of reality that will accompany us until the end of correction (Gmar Tikkun). We will always feel that changes take place somewhere outside. Similarly, this is how we imagine this world existing somewhere outside us, although it is all inside.
Relative to the Light, we also say that the Light acts on us from outside, rather than saying that informational genes are constantly working in us, taking turns one after the other. And through these new genes, I sense the Light, meaning that I react to it in new ways.
The Light itself does not change at all: It is completely invariable. There is no division into five or ten Lights, or that the Light is entering or exiting the desire; everything exists only in the perception of the vessel to the degree of its impression on what fills it. The creature’s sensation of its fulfillment is called the Light.
We talk only about matter and form clothed in matter. Matter is the desire to enjoy. And as to the form clothed in matter, we call it “Lights,” “properties.” We talk about nothing else except these two concepts, neither an abstract form nor the essence. That is, the Light is the impression of the vessel on some unknown fulfillment. How does the vessel know that there is something inside it? It knows according to the results….
Similarly in our world, if I suddenly come down with a fever, I go to a doctor, and he says that I have a virus. But how does he know what happened to me? He checks external symptoms that point to some internal processes.
From the 3rd part of the Daily Kabbalah Lesson 6/20/2011, Talmud Eser Sefirot