At this stage of history we only have the ability to draw new souls from BY'A, which are the of Neshama, Ruach, and Nefesh, as is known.

BY'A is the abbreviation for the worlds of Beriya, Yetzira, and Asiya. They correspond to Neshama, Ruach, and Nefesh, respectively, as is known. It is only these levels of the soul body of Adam that can emerge as new souls, until the time of the Resurrection of the Dead.

However, in the future, after the Resurrection of the Dead, higher "new souls" will descend from the world of Atzilut.   They will be from the Atzilut level of the soul of Adam, which is called Zehira Ila'a [Upper Emanation], as we will explain in future discussions.

This is the secret of what is written in the Zohar, (Pekudei 253a) "From the time the Temple was destroyed, souls have not entered the Sanctuary of Love [Heichel Ha'ahava]."

The Ari will now give this teaching of the Zohar a unique interpretation based on the topic at hand.

New souls that are born from the Unification of Face to Face from Atzilut have not entered there [the Sanctuary of Love]. However, new souls from BY'A can come [into that place] even in these days after the Destruction of the Temple.

All the other souls that come into the world were included in the soul body of Adam after he was created by the Unification of Back to Back.

Since Zu'N are Back to Back…the kelipot are afraid to approach her face…

New souls can come from BY'A, but not from Atzilut. All other souls that come into the world are old souls. They are all born from the Unification of Back to Back.

They need to be separated from the aspect of Back to Back, and turned to Face to Face. Z'A and Nukva (abbreviated: Zu'N) are originally manifested Back to Back, as mentioned previously. The Ari explains the reason for this.

The kelipot want to suck light and nourishment from Nukva. She is susceptible to them because she does not contain great light in the first place and "Her feet go down to death…" (Proverbs 5:5). If Zu'N were Face to Face, then the back of Nukva would be exposed, and the kelipot would be able to take hold there, G‑d forbid. Since Zu'N are Back to Back, and her face is projected outward, the kelipot are afraid to approach her face.

Also, when they are Back to Back they are joined together with one Back, like what is found sometimes among Siamese Twins. Because they are joined together by one Back the kelipot cannot insinuate themselves between them to attack the back of Nukva.

The kelipot suck when there is a little bit of light, but when there is a lot of light it is their nemesis. When Zu'N receive greater light from above, then the threat from the kelipot is diminished. It is then possible to expose her back, and allow them to turn Face to Face in order to accomplish the Unification of Face to Face.

However, since they were joined by one Back, in order to turn Face to Face a process that the Ari has compared to surgery must separate them. Specifically, Z'A must receive sufficient light from above to enable the shared Back to double, one for him and one for her. Then they are separated sefira by sefira, until they are two, separate, independent partzufim. This is the first stage of the process called nesira - the Separation. It is a very important concept in the Lurianic Kabbala.

He gives her light and builds her up until they are both Face to Face…

Nesira plays an especially important role in the intentions of the weekday meditative prayer in the word be'ahava - "in love" - which appears in the first blessing of the Standing Prayer. Z'A began with a lot of light, and Nukva with only a little. During nesira he gives her his light, and she receives an additional enormous amount from above. At that time he is asleep like an anesthetized person in an operation; he is dormant, nearly non-existent. At the end of the nesira he receives once again an influx of light directly from above. She is diminished again but is then opposite his face and not connected to his back. Little by little throughout the rest of the prayer, he gives her light and builds her up until they are both Face to Face, receiving more or less equally from above, and ready for the Unification of Face to Face. This is be'ahava - in love!

It seems that the Ari has deliberately made this allusion because of his explanation of the teaching of the Zohar concerning the Sanctuary of Love. Since the old souls from the level of BY'A can enter the Sanctuary of Love, they can be separated and turned towards each other to enable the Unification of Face to Face that will give birth to them anew. The souls of Atzilut, however, cannot enter the Sanctuary of Love at this time.

In summary, all old souls come from him [from Adam].

All old souls come from the soul body of Adam. New souls do not come from him specifically because they are new, as if they were never in the world before. Old souls from BY'A can be elevated, renewed, and reborn as new souls, even in this period from the Destruction of the Temple until the Resurrection of the Dead. New souls from the level of Atzilut will only come into the world after the Resurrection.

[Commentary by Shabtai Teicher.]