What is it about the Aba Ve Ima of the world of Nekudim that makes them the “head” of the world of Nekudim with respect to the body, the ZON (Zeir Anpin and Nukva)? They have the illumination from the Upper Partzuf, Keter. This illumination is protection from egoistic desires; it’s the Light of Hassadim guarding them from the desire to receive pleasure. Even if this desire emerges suddenly, the Light of bestowal protects them from egoistic reception. For this reason, Aba Ve Ima is the head.
What is the difference between the head and the body? In the material world they are made from different material: the brain and the flesh. However, what’s the difference between the spiritual head and body (Rosh and Guf)? How does thought differ from desire? Isn’t desire the only thing that was created by the Creator?
The spiritual head is the separation from the desire to receive pleasure that allows a person to carry out actions above the desire to receive. By receiving an illumination from Hassadim, the Light of bestowal, the desires or spiritual vessels (Kelim) become the head. This Light allows them to disconnect from the desire contained within them and perform a calculation above it, as though looking from the side objectively, like an independent observer.
A head is the part where an objective decision can be made. This separates a human being from an animal and, in general, from all of nature (the still, vegetative, and animate). Spiritually, the differences lie in the fundamental essence and not in the material itself, like in our world.
From the 3rd part of the Daily Kabbalah Lesson 7/5/10, Talmud Eser Sefirot