(והנה בחינת הצמצום והסתר החיות נקרא בשם כלים, והחיות עצמו נקרא בשם אור
(The tzimtzum and concealing of the life-force is called in kabbalistic terminology kelim (“vessels”), and the life-force itself is called or (“light”), which signifies revelation.
שכמו שהכלי מכסה על מה שבתוכו, כך בחינת הצמצום מכסה ומסתיר האור והחיות השופע
For just as a vessel covers that which is within it, so does the tzimtzum cover and conceal the light and the life-force that flows into created beings, and this tzimtzum makes it impossible for them to perceive the G‑dliness that is vested within them.
והכלים הן הן האותיות
The kelim are verily the letters of the Ten Divine Utterances (or their substitutions and transpositions, etc.) which are the life-force of created beings,
ששרשן ה׳ אותיות מנצפ״ך
and [all these letters] are rooted in the five letters מנצפ״ך
It is explained in the Kabbalah that these are the source of all letters, —
שהן ה׳ גבורות המחלקות ומפרידות ההבל והקול בה׳ מוצאות הפה, להתהוות כ״ב אותיות
since they represent five degrees of Gevurah i.e., five restraining forces that divide and separate the breath and voice in the five organs of speech, thus enabling the twenty-two letters to be formed.
Just as the five physical organs of speech divide sounds and letters into five separate categories (labial, guttural, etc.), so too do the five spiritual levels of Gevurah give rise to the twenty-two supernal letters.
ושרש הה׳ גבורות הוא בוצינא דקרדוניתא
The source of the five levels of Gevurah is termed in the Kabbalah Butzina deKardunita, which is Aramaic for (lit.) “light out of darkness,” signifying a level of concealment that transcends light.
שהיא גבורה עילאה דעתיק יומין
This is the supernal Gevurah of Atik Yomin, the spiritual level of Keter that transcends all Worlds, including Atzilut;
ושרש החסדים הוא גם כן חסד דעתיק יומין
and, correspondingly, the source of [the various levels of Divine] kindness is Chesed of Atik Yomin,
כידוע ליודעי ח״ן)
as is known to those well versed in the Esoteric Wisdom,) i.e., the Kabbalah.
Since the tzimtzum and the letters (on the one hand) and the revelation of the Divine light and life-force (on the other hand) both emanate from the level of Atik Yomin, it follows that the tzimtzum does not effect an objective concealment, as viewed from their common source Above. For, as previously explained, “No entity can conceal itself from itself.”
Thus, tzimtzum affects and is only felt by created beings, who because of this concealment are unable to perceive the Divine life-force that continuously creates them. This is necessary in order for them to think of themselves as independently existing — a state which must be felt by them if they are to “tangibly exist.”
In truth, however, they are utterly nullified within their source Above.