Name of G-d
Since in Hebrew there are no vowels, it is impossible to know how to pronounce, much less to understand, the four letters - the Tetragrammaton - by which G-d's identity is signified in the Torah: Yod Hey Vav Hey.
Around this fundamental unknowability grows an elaborate metaphysical tradition, the central mysticism of Judaism. Throughout their implicated histories, Judaism and Christianity resolve into ontological opposition: in Christianity, the goal and assumption is the knowability, accessibility, and intimacy - the nameability - of the Godhead. For the Jews, G-d is the ultimate unknowable. Perhaps this explains the violence in the hyphen of Judaeo-Christian.Christianity, assuming the knowability of the Divine, proceeds to evolve a science of sureness. Judaism, assuming the multiple truths of its G-d, proceeds to evolve a system of knowing that requires continuous interpretation, founded not even on quicksand but on quarks, the substrate of physical uncertainty itself.
The reason you cannot know is no fault of your own, your point of view, or your method of inspection. You cannot know because there is fundamental unknowability. When Moses asks G-d how he should name Him when he brings back G-d's message to the Hebrews in Egypt, G-d answers with an untranslatable Tetragrammaton: "Call Me by these four letters [without vowels]."
The four letters indicate some transcendental declension of the verb "to be" in a dynamic state. This "becoming" quality is essential to Judaism and the Hebrew language itself, especially in contrast to the static perfection that is the ideal of Greco-Christian culture. As Thorleif Borman shows in Hebrew Thought Compared with Greek (1960), this distinction between Hebrew and Greek thought, the first as unfolding, the second as static, is intrinsic to the deep structure of the two languages.
Ironically, what disguises this difference between the classical Greco-Christian and Jewish assumptions about the (un)knowability of the universe/Godhead is a simple trick of translating between alphabets: when these four Hebrew letters are translated into Greek and later Latin, they are mistakenly vocalized - vowels are provided arbitrarily - so they become "YAHWEH."
This difference summarizes and disguises the (suppressed) difference between alephtavian and alphabetic knowing. The
stands for the G-d who turns the Divine Face aside and conceals the True Name even as He recedes, calling out over His shoulder to Moses on Mount Sinai, or forcing Moses to turn his face aside. On the other hand,
stands for a march of dragon's teeth towards the Empire of Knowing, naming names, summoning a familiar and knowable God, creating (the illusion of) presence and of Being, and a firm belief that striving for certainty leads to certainty, and not to vanity.