Rabbi Moses Cordovero
The parable about this [is as follows:] When a beam of sunlight passes through a window into a house illuminating the opposite wall of the house, and due to its excessive brightness no one in the house is able to bear it. Their eyes become dim from looking at the sun because it[s light] is great and extremely bright, until they must make a very large shade, so that the light might shine to the opposite wall, and those who are standing in the house might obtain the benefit of the light, and not its detrimental effects. But, due to the great brightness of the sun's light in its power and strength, despite the fact that the light has [now] been made somewhat more pleasant, as well as hidden and somewhat concealed, nevertheless, due to weakness of sight, those standing in the house require a second screen, and then a third to that one, up to ten.
But now, if someone enters the house to benefit from the light that is shining through the shade, and asks why the number of the shades is such and such, and not something else, refute his arguments. We would say to him that it is because of his great stupidity that he asks about this. For since the intention of the matter of the screens is to put the matter of the light right, in order that it might be made more pleasant for the sake of the eyes of those who see it, therefore if one were to diminish the [number of] screens, the eyes of those who see it will be darkened due to the amount of light, and it will cause damage. But if one were to add to them [the screens] the light would be darkened, and the pleasantness of the light would not reach those who see it and the eyes darkened by the windows [that should have given light].
The intention of this chapter is to explain that the matter of this order [of the sefirot] does not relate only to all the ten sefirot in their generality, but also to their particularity. How? If we wish [we may] say [that there are] nine [sefirot] from Keter to Yesod and nine from Yesod to Keter. And similarly, eight from Hod to Keter and eight from Keter to Hod, and likewise, seven from Hesed to Malchut and seven from Malchut to Hesed. But this is not all: [It] even [applies to] to each [individual] sefirah, as we will explain. ...from Pardes Rimmonim ('Orchard of Pomegranates'), Gate 2 ('The Reason for Emanation'), chapter 6.
The meaning of them is that just is there is a light reflecting the illumination from Malchut, so too there is reflected illumination from Yesod, and likewise from Hod, and so on, for all of them. And just as there is a direct light from Keter, so [there is one] from Hochmah, from Binah, from Hesed [and so on], for each sefirah is the source of all below it and each sefirah is a mirror which the light [coming] from above strikes. Then the light is reflected until, by this route, the lights ascend, directly and by reflection, innumerable times, as the researcher will understand with his intellect if he applies his mind to what has been hinted at [here].
In the Righteous One [=Yesod] there are eighteen [The Tikkunei HaZohar says that Yesod represents the Eighteen Benedictions] and I say that there are nine from the bottom up and nine from the top down. But one may not say that the matter is thus, namely that when one reckons and counts [this] sefirah from the top down that makes nine and when one counts from the bottom up that makes nine, for in that case one never [actually] adds up more than nine, so how can you count eighteen? However, it is certain that Yesod is in the mystery of the direct light and the reflected light, and as Malchut is to the number ten so too Yesod is to the number nine. Similarly, Hod to the number eight. But these are not the same, for every number is a mystery in its own right and an aspect in its own right. So, too, the direct light and the reflected light are not one matter.
And the reason is that the direct light is of the mystery of the light in its essence, the foundation of the structure of emanation. However, the mystery of the opposite light does not illumine as the mystery of the direct light does, just as the image of a beam of sunlight is not the same as that which is reflected back to itself by virtue of its [original] power. For the reflection is one product out of its many products caused by one [of the many properties] of those things that receive it. But the beam of the direct [light] is itself a beam in its own right, and as such may be compared to emanation. So, just as the light when it is reflected back by an [ordinary] reflector or a mirror is not like that which is reflected back by a shiny mirror of cut crystal, so too in the matter of the mystery of the light that is reflected back from Malchut or from Yesod or the like. Similarly, [any] variation in the light will be in accordance with the difference in the colours in the mirror which receives the beam and reflects the light back to its original source....