It is written in The Study of the Ten Sefirot (Part 3, Chapter 3, Items 4-5) that in the world of Atzilut, it is the light itself. It seems to me that his intention is that this is not so with the light that shines in the world of Beria, which is called “a light of Tolada [result/offspring],” and not the actual light.
We should interpret that Atzilut is called “private Providence,” where it is considered that “He alone does and will do all the deeds.” For this reason, the light that shines there is essential light, without any participation of the lower one. But in the separated BYA, where there is the sorting of good from bad, it is called “reward and punishment.”
Hence, the light that shines is through the association of the Emanator and the emanated, which is a partnership. This is why it is called “a light of Tolada,” as it is born out of two causes. This is unlike the world of Atzilut, where there is no partnership, meaning the lower one does not assist in anything. This is called “Evil will not dwell with you,” where there is no sorting; this is why it is called “private Providence.”
This is the meaning of what is written there, that the Masach [screen] makes a Parsa [slicing/partition] between Atzilut and Beria, so that BYA are below the Masach, while in Atzilut, there is no Masach at all.
At the same time, it is explained in several places that there are Masachim [pl. of Masach] in Atzilut, as well—a removing Masach in Bina, and a window and a narrow crevice. The explanation is that this is only with respect to BYA, but with respect to Atzilut, there is no distinction whatsoever.
The meaning is that with regard to the souls in BYA, which is reward and punishment, they feel that there are Masachim, but when BYA ascends to Atzilut and they are rewarded with private Providence, they see that everything is unity and there are no Masachim at all there.