Since the intention was to bring forth evil, the upper levels were in the process of separating from the lower levels, where there was a corresponding increase in the degree of concealment. This was precisely what distinguished them from the upper levels, because the concealment on the lower levels was so intense that evil could emerge from them, which was not the case on the earlier levels.
The explanation of all this is bound up with the idea discussed earlier that everything which acquires its own independent function acquires its own name. Accordingly, this lowest level should not have been a separate aspect in itself but should rather have been subordinate to the function of the other parts which departed from it, and then its mission would have been like theirs. Instead of producing evil, it would have served to complete the earlier levels. But clearly, the reason why we call this lowest level a level on its own is that the light found there is on a level lower than that of the previous level, even though initially the lower level also came into the overall category of the first. This is the gradation that we say took place here.