There is one infinite creator, the cause of causes and the maker of all. He is not one in a numerical sense — since He is not subject to change, definition or multiplicity. He is one in that the number one signifies an independent unit and is the basis of all numbers; the number one is also contained in all numbers. Similarly, the Creator is actually within everything, and everything is within Him. He is the beginning and cause of everything. The Creator does not change, and therefore one cannot add or subtract from Him.

Moreover, His existence is necessary existence (i.e. it is not contingent upon anything else), in the same way that the number one is a requisite for the existence of any other (whole) number. If the number one would cease to be, every other number would also cease to exist. However, if other numbers disappeared, one would continue to exist. There are properties of the number one; similar qualities apply to the Creator. Even if the act ceased to be, the One who acted remains. Because His being is not contingent upon the existence of anything else, were they to cease being, His existence would continue.

The unbounded revelation of G‑d underwent a profound constriction

Prior to Creation, there was only the infinite revelation of G‑d which filled all existence. This is called the Or Ein Sof — the Infinite Light — which is not G‑d Himself, only His infinite revelation of Himself. Within this infinite revelation, limited beings could not possibly exist. Accordingly, there was a progressive lessening and constricting of the Or Ein Sof, making room for limited existence.

This progressive constriction, called tzimtzum, brought about various planes of reality — called, in Kabbala, the five worlds. Each "world" is a certain level of concealment of G‑dliness, of the Or Ein Sof. From the highest to lowest (i.e. from greater to lesser revelation) they are: (1) the world of Adam Kadmon, which is the primordial world, or the first level of somewhat finite revelation; (2) the world of Atzilut, (3) the world of Beriya, (4) the world of Yetzira;, and (5) the world of Asiya. The entire physical universe is the lowest aspect of the world of Asiya. In each of the worlds there is an increasingly dim revelation of the Infinite light as it descends further and further and becomes more and more concealed. It is important to note that these worlds do not occupy different geographical places. They are not geographical at all, but rather descending planes of reality.

Click here to find out what the Kabbalah for Beginners Tutorial is all about.