You need to know that there is a parallelism between the Sefirot and the main sources of the Torah:
Chochma - J
Bina - E
Da'at - RJE
Chesed - H
Din - Dtn
Tiferet - PE
Netzach - P
Hod - D
Yesod - R
Here PE is the source defined by this, a combination of E-sources, J-sources, and PE proper. Dtn is largely Devarim 12-26, a halachic corpus. H is Vayikra 17-26, a priestly, ethical, and halachic corpus. E, J, P, D are as usual (...), RJE is the composer of the combination JE, R is the redactor.
Keter is under the Or Elyon. The Or Elyon does not fit into words. Malchut, finally, is under the influence of both Yesod and Keter. Seeing that the Binyan above Yesod was finished, and that the light was effectively stopped by P, D and R, Rashbi drew light instead from Keter, Or Elyon. As a reaction, the Sitra Achra closed the channel from Keter, as it had closed the channel from Yesod, and the exile was sealed. The world was darkness.
The channel from Yesod is called the revealed Torah. The name is appropriate as it is completely revealed; also P and D, the stopping sources, are completely revealed. The channel from Keter is called the Torat HaNistar. To understand the revealed Torah, one needs Torat HaNistar. And vice versa.
