Not a great deal can be said about Yesod [the Ninth Sphere of Kabbalah], because in her are hidden the keys of the magical workings.
Now, it may be asked, if the Sphere of Yesod [of Kabbalah] is etheric, why are the generative organs assigned to this sphere, for surely their function is physical, if anything is? The answer to that question is to be found in the knowledge of the subtler aspects of sex which appears to be entirely lost to the Western world. It cannot be entered upon in detail in these pages, and it must suffice to point out that all the more important aspects of sex are etheric and magnetic. We might liken it to an iceberg, five-sixths of whose bulk is below the surface. The actual physical reactions of sex form a very small proportion, and by no means the most vital portion of its functioning. It is owing to our ignorance of this that so many marriages fail to fulfil the purpose of the welding of two halves into a perfect whole.
Excerpted from The Mystical Qabalah (1935) by Dion Fortune with permission of the Society of Inner Light and Red Wheel Weiser.