The Book of Zohar, “Lech Lecha” Item 97: The first extension is the light of Nefesh, the force from which the body is built …
A spiritually born person is called Ish, and the spiritual force that animates him, the force of his existence is called the light of the degree of Nefesh.
[It]…extends by the force of the progenitors’ light of Nefesh. This is so because by the force of the great desire of the progenitors, which is a strong agreement from their light of Nefesh, they extend the light of Nefesh of the newborn from the spiritual world of Assiya, and it clothes in the semen that they produce, and the newborn’s body gradually builds out of this spiritual light.
Just as a person is born from the mother and comes out into our world, but before that he was inside her, so we are born into the spiritual world from within. Therefore, the uterus in which we are now is a preliminary place for birth in the upper world.
The world of Assiya is the lowest of the worlds. The first spiritual birth takes place in it when our eyes and feelings open. I am called Ish in it, and my energy, my understanding, everything that animates me is called Nefesh.
Assiya is the world of action because I do not understand anything yet, I do not know, I just develop via my instinctive actions.
From KabTV’s “The Power of The Book of Zohar” #18