“The experiences of magicians over several hundred years have shown that the flow of etheric substances in the physical world increases and decreases in regular patterns. There are, in effect, tides in the Unseen, and the Moon affects these as strongly as it does the tides of the ocean. This influence is powerful enough that certain kinds of ritual work can only be done effectively at certain lunar phases. The association of the Moon with Yesod followed naturally from this.”
“Despite the common notion that sex is the most physical of activities, most of sex takes place on the etheric and higher levels. Deprived of these, sex becomes nothing more than friction, and–since the etheric aspects of sex link, through the nephesh, to the instinctive drives that energize the whole affair–not especially enjoyable friction at that.
Some of the most closely guarded teachings of traditional Cabalism deal primarily with sex. […] Sex … is much more a matter of the etheric body than the physical one. … The etheric body itself is a vehicle for the ruach, and the union of etheric bodies (which is what happens in sex) can, and often does, become the basis for a corresponding union of one or more levels of the ruach.
When this happens in ordinary life, sex becomes the basis of love; when it happens between two people who have made some progress toward the parting of the Veil, the energies of the union can rise to levels of the ruach not normally accessible, and open these up to consciousness; when it happens between two people who stand on the edge of the Abyss, the joining of the two can flower into the experience of the union of all.
The mating of lovers in this context becomes not merely a poetic simile for, but an experience of, what mystics have called–in equally sexual terms–the mating of God and the world.”
–John Michael Greer, Paths of Wisdom: The Magical Cabala in the Western Tradition, 1996, pg. 114-5.