Sefer haZohar on Emanation and the Letters of YHVH

"Rabbi Shim'on said, 'We have learned that when the blessed Holy One created the world, He carved engravings of mysteries of faith within radiances in supernal mysteries. He engraved above, He engraved below, all in one mystery of engravings of the Holy Name, YHVH, ruling through its letters above and below. Through this mystery worlds were consummated, the upper world and the lower world.

"The upper world was consummated by mystery of the letter Yod ─ primordial supernal point emerging from within the concealed and hidden, which is unknown unsusceptible to knowing, and completely unknowable, mysterious ascension of Ein Sof. From this concealment shone a single radiance ─ subtle, concealed, comprising within itself the totality of all lights. That concealed radiance was struck by one who did not strike, illumined by one who did not illumine, and then it emitted one radiance ─ bliss in which to delight, radiance in which subtle concealed radiance may be secreted..."

-- Sefer haZohar, 2:127a (transl. D. Matt)

Rabbi Shim'on continues his discourse, but consider: this portion of text is meant to be recited aloud as a blessing. It is a theurgical exercise that opens the subtle energy channels inside one's own Tree.