Nukva means "the female," the partner. It is the partzuf of Malkhut, the final heh of the Name; Shaar HaKlalim also calls her Bat, "the daughter." In the world of Tohu, she was only a point, which did not break entirely like the others; after the repair, says the text, she merited becoming a complete partzuf.
Her birth is unusual. Shaar HaKlalim explains it: her head comes forth from behind Zeir Anpin, and not face to face, because the back is the place of judgments, where the outside forces can take hold; the two backs therefore cling to each other, so that those forces have no grip. It quotes the verse of Lamentations: "He drew back His right hand before the enemy." Etz Chaim also reads the Psalm: "Behind and before You formed me."
Then she grows. At first a point, during conception she reaches the size of the Yesod of Zeir Anpin, during nursing that of Tiferet, and with maturity she becomes a complete partzuf. Then comes the nesirah, the "sawing": the two are separated so that they can meet again face to face. Etz Chaim reads in this the verse of Genesis: "the L-rd G-d cast a deep sleep upon the man, and he slept; He took one of his sides."
The Nukva has two faces, which Etz Chaim names after the wives of Jacob. Leah, above, stands behind the head and chest of Zeir Anpin; Rachel begins at the chest and goes down. Where Leah ends, Rachel begins, for, according to the saying of the Sages, "one kingship does not touch another, even by a hair's breadth." Their unions are tied to the prayers of the day: at night with Leah, with Rachel at the time of the morning prayer. And Shaar HaKlalim specifies that the union of Zeir Anpin and the Nukva depends on our good deeds, our prayer, and above all the Shema.
Cordovero, in the Pardes, calls Malkhut "the third concealment," named the Nukva of Zeir Anpin. For him too, she is the one who receives all that is above; but the account of back to back, of the sawing and of the growth belongs to Etz Chaim.
Keep the lesson of this account: the relationship is built in stages, from back to back to face to face. And according to Etz Chaim, this passage does not happen without us: the prayer of Israel takes part in it.
