Let us accept the term AIN as representing That of which Nothing is known, nor can be known, except through the positive manifestations which arise form It. When we attempt to imagine the AIN SUPH-Limitless Space-our minds tend to rush on and on, only to fall back before the Profundity of the Great Deep; yet we have to admit the possibility of Infinite extension in space. In my opinion this is due to the fact that we are only able to extend the fine material substance of the mind to a certain limit, after reaching which there is NOTHING for Us unless we succeed in developing fresh Power to drive that limit further back and so to extend the actual substance of our being accordingly.If Life is the Substance of Light, the Life itself is to be considered as the most subtle substance in our make-up, while it would follow that the more this substance is extended, the greater will be our Illumination, the further our range of vision, and the wider our Sphere of Consciousness.
With these thoughts in mind let us attempt to obtain a more complete Understanding of the Primal Process, which is still "going on" Here and Now.
When the AIN SUPH AUR became concentrated upon a Single Center, it compressed the Light into the Substance of Light, which is Life. Or, in other words, the Concentrated Light became an inconceivably powerful Force or Energy in the center of Kether. This Pure Being, or Living Substance, owing to its reaction from the Invisible Center, tends to expand towards Infinity. This gives us the idea of the Substance of the Universe ever expanding , ever occupying more and more of the Limitless Space of the AIN SUPH, while the Primal Centralizing Urge still continues to contract upon the Infinitely Small, or the AIN.
Kether is then the junction of these Two Infinites, but particularly represents the concentration of the Light to a Point on its way to the Infinitely Small, while Malkuth, the Tenth Sephira and Sphere of the Elements-which the Qabalists say is one with Kether-is the Substance which is ever expanding and, so to speak, gradually FILLING UP THE NOTHINGNESS of the AIN SUPH. So we may consider Kether as the Light and Malkuth as the Substance, while the complete Sphere is composed of LIVING SUBSTANCE. This represents the Macrocosmic Universe, but it is every BECOMING GREATER AND GREATER in extent, and driving back, so to speak, the Nothingness of Chaos. Man, being made in the Image and Likeness of God and of the Universe, has the same infinite possibilities of growth in Consciousness, as the Force of the Spirit extends the substance of his mind to wider and wider fields of thought.
Yet the whole existing Universe is the result of the One Thought of God, and it progresses according to the Order of Pure Reason, as indicated in the Qabalah. All the Sephiroth and Paths have their place according to this Order, within the Sphere of the One Substance, and represent the manifold possibilities of the action of the Life Force upon that Substance and the different manifestations of that Substance under the Influence of the Life Force.
In other words, WITHOUT [i.e. outside] the manifested universe is the Infinite Body of Nuit; at the CENTER of All is the Infinitely Small and unextended Essence of Life, or Hadit. The Contraction of Nuit upon Hadit and the Expansion of Hadit into Nuit are constant forces. The Finite Universe, or Ra-Hoor-Khuit, the Ever-Coming Son, is bounded by an EVER WIDENING CIRCUMFERENCE which is always exactly
BETWEEN the Infinitely Great and the Infinitely Small. Kether and Malkuth-Spirit and Matter-together represent this Universal Sphere, while Tiphereth, the Central Sphere of the Tree of Life, must always correspond to Ra-Hoor-Khuit within them; a Sphere HALF-WAY between the Center and the Circumference.
In Nature we may consider the finite representatives of these two Infinites to be the smallest known particle of matter as the Center, the widest expanse of the Star Universe as the circumference, and the Central Sun as their child.
In Man we find all these possibilities, both infinite and finite. The true Center of his being is Hadit whose representative is the tiny Spark of Pure Spiritual Light; the substance of his Mental Body is only limited by the Bounds of the Universe, and these ever recede towards Infinity. His physical body is, however, quite small, while his heart, which regulates the life of that body, is in a mystical sense capable of comprehending the "Light in Extension" of the Sun of his being, which is the soul.
Thus Man is composed of body, soul, and spirit, and the soul is the mediator between the spiritual and material.
The Universe is composed of Malkuth and Kether, with Tiphereth as the Mediator between them, while, in a still greater sense we may consider Nuit and Hadit, the Two Infinites, with the Whole Living manifested Universe of Ra-Hoor-Khuit, as their Ever-Coming Son, the Crowned Child and Lord of the Aeon.
Source: hermetic.com