“The concept of an infinite, perfect supreme being that cannot change, a concept absent from Jewish thought in antiquity, is dominant in both philosophy and kabbalah. This concept, which was expressed in the most powerful terms by Aristotelian thinkers when they discussed the primal cause or the unmoved mover, was accepted wholeheartedly by Jewish medieval thinkers. Kabbalistic terminology often used the term “ein sof,” no end, infinite, to designate this supreme entity.”
“The process of emanation that brought forth the system of the sefirot was the kabbalistic answer to the question, “How can anything different emerge from the unchanging and eternal divinity?”
“Many kabbalists insisted that the ein sof is not indicated by any biblical phrase, because its perfection and unchanging character put it beyond language, even divine language … The realm of ein sof in the kabbalah is therefore beyond language, beyond any kind of description, and essentially it is not different from the rationalistic designations of the infinite supreme eternal entity.”
“This and other such systems attempt to build a bridge between the timelessness of the ein sof and the sefirot, which exist in time … The most important aspect of ein sof in kabbalistic thought is as the ultimate source of the flow of the purest divine light (shefa) that constantly provides the power to exist in both divine and earthly realms. Emanation is not a one-time event, but an ongoing vital process that maintains the existence of all beings.
“The kabbalists differed from the neo-Platonists in the intense dynamism and mythological elements that they introduced into their system, especially in the lower realms of existence, and in their belief in the capacity of human deeds and behavior to influence processes in the divine world.”
As above, so below, and vice versa.
–Joseph Dan, Kabbalah: A Very Short Introduction, 2006, pp. 39-41.