The most philosophically distinctive feature of Kabbalistic thought is not its cosmology but its theory of language. For Kabbalah, Hebrew is not a human language, one of many arbitrary systems for tagging concepts with sounds. It is the divine language, the linguistic structure that is constitutive of reality itself, not merely descriptive of it.
This position has a name in contemporary philosophy of language: linguistic idealism or ontological linguisticism, the thesis that language does not describe a pre-linguistic reality but constitutes it. The Kabbalists arrived at a form of this thesis millennia before it became central in Western philosophy through Heidegger ("Language is the house of Being") and the later Wittgenstein (meaning as use within forms of life).
But Kabbalistic linguistic philosophy has has that distinguish it sharply from Western versions. First, it is specific: not language in general but the Hebrew language specifically, and not the semantic level of Hebrew (its vocabulary and meanings) but the phonological-graphological level (the specific shapes and sounds of the 22 letters, their numerical values, gematria, and their physical positions in the mouth when pronounced). Second, it is embodied: the letters are realized in the human body as well as in the cosmos. Third, it is meditatively accessible: by attending to the letters, visualizing them, vocalizing them, permuting them according to the methods described in Sefer Yetzirah, the practitioner can gain access to the creative energies they embody.
The technique of tziruf (letter-combination) is the core contemplative practice derived from Sefer Yetzirah. By systematically permuting the 22 letters, combining them with each other and with the divine Name, the Kabbalist was believed to gain access to the primordial creative processes themselves. The 13th-century mystic Abraham Abulafia developed an elaborate system of letter-combination techniques that he called the "science of combination", a form of contemplative practice aimed at the dissolution of the ordinary self and union with the divine through the medium of the letters.
The philosopher Gershom Scholem, the great 20th-century historian of Jewish mysticism, analyzed the Kabbalistic theory of language in On the Kabbalah and Its Symbolism (1965). He argued that what distinguishes Kabbalistic linguistics from both allegorical interpretation and rational philosophy is its conviction that divine language has an absolute, non-conventional relation to reality. The Torah, for the Kabbalists, is not a text that describes divine reality in human language; it is an expression of divine reality as language, the divine name articulated in narrative form. Every letter carries infinite depths of meaning that can never be exhausted by any human interpretation.
This connects to a contemporary philosophical debate about whether there can be a non-arbitrary connection between signs and what they signify, a question that runs from Plato's Cratylus through Saussure's insistence on the arbitrariness of the linguistic sign to Derrida's deconstruction. Kabbalah represents the most fully developed tradition arguing for the non-arbitrariness of the fundamental elements of (one particular) language, and doing so not as naïve folk belief but as a sophisticated philosophical-mystical system with internal logical structure.