I'll describe the general purpose first: numerology allows us to connect any two objects. This theoretically gives us a great advantage in prayer and meditation, since we can connect anything we see to the object of thought. For other uses, see here, sections I and II. (See also Conspiracy Theorists, accidental demon summoning by.)
Now, by these methods we can classify anything imaginable using the Tree of Life diagram (earlier version here.) I'll address the unimaginable in a second. The diagram shows the ten Sephiroth -- literally numbers or countings, but the word has come to mean emanations of God -- and their relationships with each other. Sephirah ten corresponds to the world we live in (well, most of the time). To continue my last post, we can describe the Sephiroth as Earthwards or Onewards relative to each other. We'd probably want to distinguish between 'Earthwards in the diagram', like Nine relative to Six, and 'Earthwards in numerical order', like Eight relative to Seven. Note that occultists call the numerical order of Sephiroth "the lightning bolt", for obvious reasons. Note also, that no path connects Sephiroth Three and Four. This gap represents the "Abyss" between our world and "God". The first three Sephiroth, starting from One, correspond roughly to the Hypostases of Plotinus. Understanding goes with the Soul (the Neschamah, really, but never mind that now) while Wisdom goes with the creative Intelligence or Logos. Beauty receives a ray from each of these three Onewardmost spheres.
Now, I promised to mention the unimaginable. In orthodox Kabbalah, as I understand it, all these emanations come out of the Limitless Light (Ain Soph or Ain Soph Aur) by way of the One. Orthodoxy also teaches that we can best represent Ain Soph by using the negative, Ain (Nothing). Names of God (and images, if any) would better correspond to the emanations. This helps to explain why Aleister Crowley assigned Ain Soph to the number Zero. At some point, unless I get permanently side-tracked, I'll explain a little more of his viewpoint. I also want to describe the "planetary" correspondences of the Tree, with something resembling an explanation, and I have some remarks on Mercury in particular. That last bit will probably find its way here even if y'all show no interest -- I may spare you some of the rest depending on the response.