Answer: There is a prohibition on incest because there cannot be a connection between the upper Partzuf and the lower Partzuf in the spiritual body. The two Partzufim that are opposite one another mustn’t ascend to the same level since it leads to the shattering of the vessel.
On the whole this is also reflected in our world according to the principle of root and branch. Basically the Torah doesn’t speak about the corporeal states of the body in which we continue to keep the laws of the spiritual world according to the principle of “in His image and in His likeness,” but in the corporeal world, these are no longer laws but customs.
From the Kabbalah Lesson in Russian 12/6/15