The Reality Contained in the Science of Kabbalah
Kabbalah uses only names and appellations that are concrete [attained in our senses and then examined in our mind] and real [revealed to us to the extent of our correction]. It is an unbending [absolute] rule for all Kabbalists that, “Anything we do not attain [clearly, in our corrected qualities], we do not [it is impossible to] define by a name and a word.” [It is because a name explains the quality of the object being attained, and that quality is attained to the degree of similarity to the object’s qualities, according to the law of equivalence of form: Only similarity is attained.]
Here you must know that the word “attainment” (Heb: Hasaga) implies the ultimate degree of understanding. It derives from the phrase, “that thy hand shall reach” (Heb: Ki Tasig Yadcha). That means that before something becomes utterly lucid, as though gripped in one’s hand, Kabbalists do not consider it attained, but understood, comprehended, and so on.
– Baal HaSulam, “The Essence of the Wisdom of Kabbalah”