The desire is the root of the mind and not the mind the root of desire.
Baal HaSulam, “Peace in the World”
The thought serves the desire, and the desire is the “self” of the person.
Baal HaSulam, Shamati [I Heard], Article no. 153,
“The Thought Is an Upshot of the Desire”
The mind is enslaved and serves the desire.
Baal HaSulam, “Introduction to The Book of Zohar,” Item 21
A thought is an upshot of the desire. A person thinks of what he wants, and does not think of what he does not want. For example, a person never thinks of his dying day. On the contrary, he will always contemplate his eternity, since this is what he wants. Thus, one always thinks of what is desirable for him.
However, there is a special role to the thought: it intensifies the desire. The desire remains in its place; it does not have the strength to expand and perform its action. Yet, because one thinks and contemplates on a matter, and the desire asks of the thought to provide some counsel and advice to carry out the desire, the desire thus grows, expands and performs its actual work. It turns out that the thought serves the desire, and the desire is the “self” of the person. Now, there is a great self or a small self. A great self dominates the small selves.
He who is a small self and has no dominion whatsoever, the advice to magnify the self is through the persisting with the thought of the desire, since the thought grows to the extent that one thinks of it.
And so, “in His law doth he meditate day and night,” for by persisting in it, it grows into a great self until it becomes the actual ruler.
Baal HaSulam, Shamati [I Heard], Article no. 153,
“The Thought Is an Upshot of the Desire”
The very essence of the soul is a will to receive, as well. 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