From Innerpedia - Encyclopedia of Torah's Inner Dimension - Chassidut and Kabbalah
Kah (י-ה) is one of the Names of God.
In Kabbalah, the Name Kah is generally associated with the sefirah of chochmah.
As the first two letters of Havayah, the yud corresponds in particular to chochmah while the hei corresponds in particular to binah, the "two companions that never part." These two letters are also referred to as the concealed dimension of Havayah (in relation to its last two letters, its revealed dimension), implying that the Divine providence which derives from the level of Kah is generally (or initially) unfathomable to the mind of man. Thus, suffering of all kinds, though ultimately for the good (and even now, essentially good, were we able to perceive it), is said to derive from Kah.
In apparent paradox, throughout the Psalms of David, the praise of Kah is repeatedly expressed (especially by the phrase hallelu-Kah). The entire book of Psalms concludes with the verse: "Every soul shall praise Kah , hallelu-Kah." Our sages interpret "every soul" as "every breath"--implying that each and every breath of life should be infused with a consciousness of praising Kah. In Kabbalah and Chassidut we are taught that through the sincere expression of praise, one "brings out" the praiseworthy attribute in the one praised. Thus by continually praising Kah, we merit to reveal and experience the infinite good and pleasure "hidden" in apparent suffering.
As representative of the inner spiritual state of chochmah, the consciousness (and praise) of Kah brings one to a true state of bitul, selflessness in the presence of God. This allows for infinite Divine light and pleasure to flow into one's consciousness and permeate one's entire being. This experience is referred to as that of "Eden" itself, above the "garden of Eden."
Kah = 15. The ratio of its two letters, 10 (yud): 5 (hei ), is that of a whole to its half. The Name Kah thus represents the general principle in Kabbalah of shalem v'chetzi ("whole and half"). (See Havayah, with relation to the identical phenomenon of "whole and half," the ratio of Havayah, 26, to echad,13).
The dimension of "whole" reflects the origin of pleasure in the superconscious. The dimension of "half" reflects the origin of will in the superconscious. Thus, the Name Kah reflects, from the perspective of chochmah (the beginning of consciousness), the two basic principles of the soul enrooted in keter, the superconscious.
Our sages teach us that the two letters of Kah appear in the two words for man (ish, whose middle letter is yud, the letter by which God created the world to come), and woman (ishah, whose final letter is hei, the letter by which God created this world). When the couple merits to reveal these two letters of the Name Kah, "the Divine Presence dwells amongst them" (if not, the remaining two letters of both ish and ishah spell esh, fire--"fire consumes them").
The Name Kah represents the secret of marital harmony, for in it lies the power to "sweeten" all apparent negativity, as experienced in oneself and in one's relationship to his companion. Through the power of Kah, the physical couple rises to the spiritual level of "two companions who never part."
In at-bash, the Name Kah transforms to mem, tzadik which equals 130 = 5 times 26 (the value of God's complete essential Name Havayah).
The Name Kah possesses three "full spellings" which equal 26, 30, and 35. 26 is the value of Havayah (this phenomenon is alluded to in the verse "for within Kah is Havayah, the rock of the universe" [Isaiah 26:4]; 30 plus 35 combine to equal 65, the value of Adnut. Together, 26 plus 65 = 91.