The difference between Keser and the other Sefiros:^[1]

The attribute of Keser serves as a medium between the infinite light of G-d and the attributes of the world’s. It is for this reason that it states that the attribute of Keser is not listed as one of the 10 attributes. In reference to this it states in Patach Eliahu, “and You are one but not in a calculated way.”

How the attributes are created from Keser: The creation of the attribute of wisdom from Keser is not in a way of chainlike descent of Yeish Miyeish, something from something, as applies amongst the attributes themselves. Rather, wisdom is created from Keser in a form of something from nothing, Yeish Meayin.

Every spiritual world contains a Keser: The attribute of Keser does not just exist prior to the world of Atzilus, but exists between each of the spiritual worlds of Beriya, Yetzira, and Assiya. By each of these worlds, the attribute of Keser serves as a medium between the revelation of the previous world and its demotion into the next world. The attribute of Malchus of Atzilus becomes the Keser of Beriya, while the Malchus of Beriya becomes the Keser of Yetzira. Nonetheless, there exists a difference between the Keser of the world of Atzilus and the Keser of all the other spiritual worlds as the Keser of the world of Atzilus was created through great contractions of the infinite light of G-d to the point that it had to leave an actual space which is empty and devoid of G-dliness, known as a Chalal and Makom Panuiy. This is in contrast to the attribute of Keser of all the other spiritual worlds which only require a curtain, known as a Parsa partition, to allow its creation and did not require a complete contraction and concealment of all revelation of G-dliness of the previous level. [The reason for this is because the distance between the infinite light of G-d and the spiritual world’s which are all limited in nature is infinitely greater than the distance between one world and the next. Hence, to create a world from the infinite light of G-d, an actual space which was empty of the infinite light of G-d was required, while to create one world from another, a simple partition is necessary in order to create a gradation of higher and lower worlds.]

[1] Torah Or p. 14a