Kether is the source of all, including the things as yet unmanifest. Stabilising consciousness at this sphere is the goal of human evolution.
Kether, or "The Infinite," is the crown of the tree, the peak of the spiritual realm, the assimilation of all spiritual work. It is the place where the pure energy first extends into the world and becomes recognizable as tangible reality. Kether-as-Emanation is described in the Zohar, in "P'Tach Eliahu," where, addressing the Creator, Eliahu the Prophet says: "...[You are the] Orach Atzilut, the Path of Spiritual Emanation, which irrigates the tree of the Sefirot with its arms and branches, like water that irrigates a tree causing it to grow thanks to that irrigation. Master of the Universe, You are the Primary Cause, and Producer of Results, Who irrigates the tree through the spring of prophecy. That spring is like the soul to the body, in that it gives life to the body."
Kether, forming a triad with Binah and Chockmah, balances three forces: Spiritual love and awareness (Binah), Spiritual will and purpose (Chockmah), and the infinite realized self (Kether). These three spheres could be compared to the 'Father, Son, and Holy Ghost' in the Christian pantheon.
Kether is Brahman - the impersonal, absolute existence, or Godhead, the all-pervading transcendental reality, the implicate and implicit order. Because of Maya (Key 2), Brahman is concealed from the Atman (Tiphareth).
Potentials of Kether: Solving the inner quest, revelation, divine inspiration, Samadhi, spiritual ecstasy, enlightenment, union with infinite merciful bliss. This is the completion of desire re-uniting with source. The realm of separating desire is among the lower Sephirot, having first divided out of Malkuth. Kether is called the "Crown," while Malkuth is Kingdom. Some Kabbalists envision multiple trees of life connected top to bottom, with Crown and Kingdom joined. This allows for infinitely more layers and distinctions within Creation. Concepts of Kingdom/King/Creator are explored in Malkuth.