Asiya Is Different Than Yetzira, Beriya and Atzilut
It is important to explain a difference between the nefesh of Asiya, and the rest of the divisions, Yetzira, Beriya, and Atzilut. This will also help us to answer a difficult question: How can a person, whose root is in malchut of Asiya, be able to ascend to keter of Asiya? Since [every Jew must reincarnate until all the aspects of NRNCh"Y are completed], then by necessity every Jew will ascend to the keter of Asiya, [then eventually] to keter of Yetzira, and [then finally] to keter of Beriya. [That being the case, then] all the other [lower] levels would [eventually] become nullified!
Since all Jews, after all their gilgulim, would eventually reach the highest level, no one would be different and no one would remain on any of the lower levels. However, that can never be the case!
There are 'leaders of thousands of Israel' from the side of keter, 'wise men' from the side of chochma...
However, this is unimaginable. Obviously, there are Jews who are on the level of malchut, and others from yesod, etc., as mentioned at the beginning of Sefer HaTikunim: "There are 'leaders of thousands of Israel' from the side of keter, 'wise men' from the side of chochma, and 'men of understanding' from the side of bina…."
Clearly the Jewish nation is composed of many types of individuals with different abilities and strengths, which are determined by their soul-roots.
However, the explanation is based upon the difference between Asiya and all the other three worlds.
For, someone whose root is in the malchut of Asiya is obviously rooted there specifically. Yet, by rectifying his actions he can purify his nefesh, level after level, until it actually reaches and becomes part of the keter of Asiya.
Nevertheless, though it ascends to the keter of Asiya, even there it remains on the level of the malchut of the keter of Asiya, since its root is on the level of malchut specifically.
His soul-root level of malchut of Asiya remains, though it ascends as a result of his spiritual improvements. Because of its root in malchut, when it ascends to the keter of Asiya it becomes the malchut of that level.
However, he must be purified until he actually ascends to the keter of Asiya, even though it will only be called the level of malchut of keter of Asiya. This is true regarding any of the levels of Asiya [to which he may ascend]: he will only be considered the malchut of that level.
For example, if he reaches the yesod of Asiya, he will only be considered the malchut of the yesod of Asiya, etc.
However, concerning Yetzira, Beriya, and Atzilut, it [the process] is different. A person whose soul-root is malchut of Yetzira, who has rectified and completed that level, also receives a ruach from the yesod of Yetzira after he has also purified and rectified the yesod of Yetzira.
As opposed to simply becoming the Malchut of the yesod of Yetzira, as was the case on the level of Asiya.
The first ruach that he had from the Malchut of Yetzira remains below [in its original place] in the Malchut of Yetzira, since that is where it belongs.
Unlike the levels in Asiya which actually ascend from level to level.
Asiya is the lowest of all worlds, and is, therefore,encompassed by the kelipot.
Likewise, when he completes the hod of Yetzira, he leaves the second ruach that he had from yesod in yesod of Yetzira, and instead he receives a ruach from the hod of Yetzira. And this is the way it continues up to the keter of Yetzira.
Since he has rectified all the levels of his nefesh from Asiya, he is able to receive ruach from all levels of Yetzira. It will be likewise with respect to the Neshama from Beriya.
The reason for this difference is that Asiya is the lowest of all worlds, and is, therefore, encompassed by the kelipot.
The word kelipot means "encasements," like the peel of a fruit, or the shell of a nut. It refers to the extreme opposite of spiritual purity and holiness, and is therefore the element within creation that makes possible spiritual impurity and sinful action. Sometimes the kelipot are called "Chitzoniyot," which means "Externalities." Being the least spiritually pure element in creation it is the furthest from light, and therefore at the bottom of all the worlds.
Consequently, even though a person has already rectified the root level of his nefesh in Asiya, still, if he leaves it on that level, there is a fear that the kelipot there will latch on to it.
Since evil has no independent existence of its own, it derives spiritual nourishment and strength from the side of holiness, but for its own evil purpose. The closer something holy is to the kelipot, the more vulnerable it is, and the more desirable it appears to the kelipot as a source of nourishment.
Therefore, [he must constantly refine his actions] until he rises as high as he can, [until he reaches his root] in the keter of Asiya.
However, in the World of Yetzira, and how much more so in the worlds above it, there is no fear of the kelipot latching on, as there was in Asiya.
The ability of the kelipot to latch on is eliminated on this more sublime level.
Hence, when a person rectifies the root of his ruach in Yetzira, he can rectify another ruach from a higher level. Then the first ruach can remain in its place, in his root. He can acquire a second from a higher place without having to raise up the first ruach to a higher place because the fear [of the kelipot latching on] is not there [in the world of Yetzira].
[Commentary by Shabtai Teicher.]