One way Qabbalists think of the Divine is by eliminating what the Divine is not. Thinking by elimination denotes that the Divine is incomprehensible – it is that is, when all that is comprehensible to the human mind has been removed. The Qabbalists gave this undefinable notion the name: Ain Soph.
There are several ways of thinking about Ain Soph.
The first is that it is the Absolute, which is the term many leading thinkers in human history chose to refer to the Divine. Absoluteness combines both: the maximum of everything (completeness, as the human mind can think of it), and the minimum of everything (the essence, also as the human mind can think of). And so the Absolute combines the entirety of as well as the essential origin of all that is – and beyond.
Another way of thinking about it, is that Ain Soph is a state of being .. the only unconditioned state of being – which is a key tenet of the oneness of God. That is, any entity (and the human being is the clearest example here) is extremely conditioned, as in limited, confined, and unaware of its powers and potentialities, when fully immersed in matter. Matter here denotes being in materialistic existence. This is why a key goal of all spiritual schools is to raise its disciples spiritually, which would make them less conditioned, in their thinking, in their manners and behaviours, and ultimately less conditioned by their being in matter. In this thinking, the higher spiritually any being is, the less conditioned it is. It follows that the Divine is the supreme state of unconditionality, of being unlimited – a state almost all ancient and axial-age religions attribute solely to the Divine.
This leads us to the third way of thinking about Ain Soph. That’s manifestation. The Qabbala, like the vast majority of advanced spiritual schools, understood creation as a series of emanations of the Divine. Or as Greek and later Islamic philosophers expounded on it in detail, creation is a series of Divine emanations through which aspects of the Divine are manifested. In this thinking, Ain Soph is the state before emanations; it preceded manifestations.
But words such as “before” and preceded” could be misleading here. This is because time in spiritual thought is not a straight line. The past, present, and future occur simultaneously, though on what kind of space-time do these occurrences take place necessitates long discussions anchored (in modern understandings) on quantum dynamics. However, in thinking about the Divine, time ceases to have any meaning the human mind can comprehend. The point here is that Ain Soph precedes emanations from the Divine, and that the preceding here denotes a status rather than a temporal progression.
This is why many Qabbalists symbolised Ain Soph by a closed eye, for when it is opened, conditioning begins, because emanations begin, materialisations out of the Source begin.
But there is another symbol for Ain Soph: the circle – the no beginning and no end, the eternal that encompasses all that is, and yet it’s a circle whose boundary is infinite. The infinite boundary signifies that the Divine is all that is. This allows for conceptualising another manifestation of the Divine, a manifestation in space. Here, the Divine fills all that is. In the reality surrounding our existence in matter, the Divine becomes the entirety of space-time.
The symbol of the circle also gives us the centre – the point of concentration of all that is in the unlimited boundary. Yet, the notion of a centre, of a point of concentration, is in itself contentious – because any concentration is a limitation, and therefore is a conditioning of the Divine. And since the Divine is by default unconditioned, the existence of the centre signals the impending dissolution of all that is (the unlimited area) into the essence of the Divine. One way of thinking about this is that the Divine manifested an aspect of it (the centre) in creation (the unlimited space), but that that aspect is temporary, conditioned by its existence in creation. Which means that the circle is not a direct representation of Ain Soph; it is a representation of the state of the world out of Ain Soph - and its destiny is to ultimately be back into Ain Soph.
This dissolution into the essence of the Divine is a fundamental tenet not only of Qabbalist theology, but of almost all religions that believe in a transcendental Divine. It is the Day of Resurrection in monotheistic traditions, the Judgement of old Middle Eastern understandings, and the stoppage of the Wheel of Necessity in Eastern philosophies.
And so the circle is a representation of a cycle, where Ain Soph expressed emanations out of it, and therefore the unlimited space manifested, and where the centre – a conditioned expression (necessarily of only aspects) of the Divine – was formed, before all collapses back into the Source that is Ain Soph, ending the whole cycle, and giving rise to the beginning of a new movement of the wheel.