Baal HaSulam, “The Essence of the Wisdom of Kabbalah”: This wisdom is generally divided into two parallel, identical orders, like two drops in a pond. The only difference between them is that the first order extends from Above downwards to this world, and the second order traverses from below upwards, precisely by the same routes and make-ups imprinted at the root when they appeared from Above downwards.
The descent was in five stages, from the “root” phase (zero) until the fourth phase, and there are exactly the same stages on the way from the bottom up. Where do these levels come from? From the desire that the Light put through the same stages of development.
So the structure is fixed and only the way it is put together is called development. Actually there is neither up nor down, we only discover the complexity of the relations between the Light and the vessel to a greater extent. First, when they were together, we could not discern it, later when it was opened, the picture became more complex because of the new details that were added to the levels of understanding of the Sefirot, the worlds, the Partzufim, etc.
Later the Reshimot (informational genes) that were left after the descent are fulfilled during the ascent.
On the whole, there is a desire, a Reshimo, and the Light that influences both of them and which builds a Masach (screen), which means the level of compatibility between the Light and the desire.
The Light is good and it is called the Light that Reforms since the desire because of the Reshimo wants something that is totally the opposite. If we still lead our desire towards the Light, we place it under the influence of the Light, and the Light turns the desire into a good desire.
Answer: It is true that there are two opposites here. If we grow in our screen and in the use of the desire, we raise the levels of thickness (the depth of the desire), from the root phase to the fourth phase. We descended the levels of the desire under the screen, and we raise the levels of the screen itself.
In any case, while moving towards this world the use of the desire decreases. Phase four below doesn’t symbolize the level of the “matter” of the desire, but the work we have to do with it.
So we begin the ascent with a small desire since we don’t feel the “matter” itself, but rather whether there is a screen above it. We attain the perception of Holiness or impurity, but not the desire itself.
From the 3rd part of the Daily Kabbalah Lesson 6/08/12, “The Essence of the Wisdom of Kabbalah”