Nefesh HaChayim, Reb Itzele's Long Annotation

Therefore, all of the rectifications of the worlds are referred to, both in the Zohar and in the writings of the Ariza”l, as “matings”519Heb.: zeevoogim. From the outset we should consider that to be strange, because it’s understood that it’s only a metaphor about spiritual matters, as in the context of a person who first, in his mind, connects two theories in the mind. And from the joining of the two concepts are born for him a new theory, based on the precursors of the two initial theories. So what brought those holy supernals to metaphorize a spiritual matter using such a physical metaphor as this?