The desire is the “self” of the person.
Baal HaSulam, Shamati [I Heard], Article no. 153,
“A Thought Is an Upshot of the Desire”
Our essence is as the essence of all the details in reality, which is no more and no less than the will to receive.
Baal HaSulam, “Introduction to The Book of Zohar,” Item 20
The very essence of the soul is a will to receive. And the difference we can tell between one object and another is discerned only by its will.
Baal HaSulam, “Introduction to The Book of Zohar,” Item 21
The primary innovation, from the perspective of Creation, which He has created existence from absence, applies to one aspect only, defined as the “will to receive.”
Baal HaSulam, “The Freedom”
All the corporeal entities in our world, that is, everything within that space, be it still, vegetative, animate, a spiritual object or a corporeal object, if we want to distinguish the unique, self aspect of each of them, how they differentiate from one another, even in the smallest of particles, it amounts to no more than a “desire to receive.”
Baal HaSulam, “The Freedom”
All the vessels and the bodies, both from spiritual worlds and from physical worlds, are deemed spiritual or corporeal substance, whose nature is the will to receive.
Baal HaSulam, “The Freedom”
Concerning the soul, which is a part of God above, the Kabbalists compared it to a rock carved from a mountain. The question arises, “How can it be said that it is the same substance as the mountain which is from His essence?” It should be interpreted that they are referring to existence from existence, hence they compared it to a rock from a mountain. The difference is in that it is part of the thing, a part which is to be called “soul.” This is the will to receive, meaning that this part is called “Creation,” meaning existence from absence.
Rabash, Steps of the Ladder, “The Substance of the Soul”
Creation refers to appearance of something that did not exist before. This is considered existence from absence. Yet, how do we picture something that is not included in Him, since He is almighty and includes all of them together? And also, one does not give what is not in Him.
As we have said, the whole Creation that He created is only the Kelim (plural for Kli) of the souls, which is the will to receive. This is quite clear, since He necessarily does not have a will to receive, as from whom would He receive? Hence, this is truly a new Creation, not a trace of which existed previously, and is hence considered existence from absence.
Baal HaSulam,
“Introduction to the Preface to the Wisdom of Kabbalah,” Item 4