Zohar Lech Lecha
There are three levels of the soul that give life force to the body. They are Nefesh, Ruach, and Neshama and their light sustains and builds the body. When a person comes with the desire to unify with a woman to procreate, the whole body is getting ready for the pleasures of the unification.
The soul level of Nefesh with the desire of the man unite to produce the seed that includes the level of Nefesh within it.
The seed that was produced from the desire of the body and the soul, pulls into it another force from the level of angels that is called ‘אישים’ (pronounced “Isheem”). The body is built from these forces. The strength of the light of the soul level of Nefesh that goes into the seed is as strong as the desire of the man and the woman during their unification. From this light, the fetus forms its body and grow.
The light of Nefesh is from the spiritual level of the world of Asiya (Action) and has a female aspect.
The development of the fetus requires the support of the level above it, which is Ruach that has the aspect of male. This force comes from the world of angels that is the world of Yetzirah (Formation). The angels have ten sefirot/levels;
מלאכים, אראלים, שרפים, חיות, אופנים, חשמלים, אלים, אלהים, בני אלהים, אישים.
In the beginning stage of development, the fetus draws from Malchut of Ruach of the world of angels that is the level of Nefesh of Ruach. The soul of the baby receives the light of Ruach and Nefesh of Nefesh. The Ruach of Nefesh is from the world of angels, אישים, and the Nefesh of Nefesh from the world of Asiya (Action).
The light of Nefesh connects to the body like bringing a sacrifice to atone for the soul. A part of the Ruach of Nefesh is given back to the angels at the level of אישים (Isheem) because it is the atonement that comes from the level of Nefesh.
When the person leaves the world that part of the Nefesh stays in the grave with the body and it allows her to communicate with other deads.
We learn that the body is made for the soul so it can be sacrificed at the end to atone for the soul.
The sperm created by the man is made in a process that transforms a desire into the matter with the force of life from the soul that goes into the woman for the process of forming the body. The type of desire of the couple at the time of unification as well as their spiritual state determines the soul that is drawn into the child and its shape.