Just as G‑d's infinite light extends downward, with innumerable expressions and unlimited revelation, so, too, it "extends upward without bounds"; i.e., [it becomes united with its Source to the point that] it becomes hidden.

[These levels proceed], concealment after concealment, elevation after elevation, causing an absence of light and revelation.

This, in general terms, is the [self-limiting] process of tzimtzum, whereby the G‑dly light becomes concealed and incorporated within G‑d's essence, His Atzmus.

Before the tzimtzum, G‑d's infinite light was overtly revealed.

As stated in Etz Chayim, "Before the emanation of any being, there was a sublime, simple light pervading the whole of existence."

That is to say that there was a boundless revelation of G‑d's infinite light: the [first and clearest] perception was of this light, while independent existence and identity were not perceptible at all.

A statement of Avodas HaKodesh will help clarify this subject:

"Just as the Infinite One possesses power with an infinite dimension, so too does He possess power with a finite dimension. For if you were to say that He possesses infinite power but not finite power, you would detract from His perfection [for there would be an area, the realm of finitude, that would remain outside the context of G‑dliness — which is impossible], for G‑d is the ultimate perfection."

G‑d's perfection is thus reflected by His capacity to encompass both potentials.

Before the tzimtzum, the unlimited aspects of G‑d's infinite light were revealed and His power of limitation was concealed.

The above quotation from Etz Chayim refers to this state when it speaks of "a sublime, simple light" (i.e., G‑d's infinite light) "pervading the whole of existence"; i.e., it alone was perceptible, while His power of limitation, which allows for a sensation of independent existence and identity, was not at all perceptible.

Through the process of tzimtzum, the infinite light was concealed, and the [first and clearest] perception was of independent identity and existence.

G‑d's infinite light was not [openly] perceived.

[Even after the tzimtzum G‑d is still one with creation, in the spirit of the verse:] — "Do I not fill heaven and earth?"

The tzimtzum applies only from our perspective; in regard to G‑d, it does not conceal at all.

Indeed, His light diffuses after the tzimtzum just as before.

As we say [in prayer], "You were [the same] before the world was created; You are [the same] since the world was created."

Both states are absolutely identical, since for G‑d the tzimtzum conceals nothing.

By way of analogy:

When a teacher communicates a concept to his disciple, he desires that his saplings [i.e., his disciples] share his conception of it.

However, in order to enable his student to cope with and internalize the concept, he may first have to entirely deflect the [overpowering] light of his own thought processes, and conceive an intellectual light that is filtered to suit the more limited capacity of the recipient.

However, though the veils and tzimtzumim by which he does this are real from the student's perspective, they do not affect the teacher at all [for he still sees the full depth and breadth of his concept even as he presents it in its less dazzling form].

In the spiritual realms likewise, the limiting aspects of the tzimtzum affect only ourselves, while concealing nothing from their Initiator. Furthermore, even in regard to ourselves, the initial tzimtzum and so too the later ones are all intended for the ultimate purpose of revelation.

As with the teacher, therefore, whose whole intent was that the recipient be enabled to receive, the tzimtzum does not really conceal at all.

Nevertheless, [it is because of the tzimtzum that] G‑d's infinite light is not overtly perceived.

Even with regard to Or Pnimi — that light and life-force which is enclothed within all existence, granting it life — there are some creations that do not perceive their life-force as being of G‑dly origin.

Even though every man feels that there is a life-force that animates him, and clearly realizes that this life-force — and certainly not his body — is the core of his existence, nevertheless not everyone perceives this life-energy as being G‑dly.

This is particularly true in the wake of the many degrees of progressive concealment that even reach the stage at which a man can say, "The Nile is mine, and I made it"; or, "My strength and the might of my hand have made me this wealth."

Such a stance results from the extreme obscuring of the light; indeed, a person's mind can thereby become so grossly insensitive that it will neither know nor feel that nature is G‑dliness.

It is G‑d's infinite power that brings about this obscurity. Just as the extension of the light until the lowest levels comes about only through G‑d's infinite power, so too it is His infinite power that conceals.

This is implied in the wording of the verse, — "It is indeed You, G‑d, Who hides." The multiple concealment is effected by "You", by G‑d Himself.

Corresponding to this concealment, there is a verse that speaks of G‑d's revelation: "G‑d's kindness endures throughout the day."

The word "day" signifies revelation.

That is to say, G‑d's revelation stems from His attribute of Chesed as expressed through the Divine Name E-l. [His revelation thus derives from G‑d Himself.]

In the same way, the fact that G‑d conceals Himself derives from "You", from G‑d Himself.

This is the dual dynamic spoken of in Sefer Yetzirah:

Omek room and Omek tachat — "the ultimate height and the ultimate depth."

Just as "the ultimate depth" (i.e., the revelation and diffusion of Divine light even in the lowliest of levels) is an expression of G‑d's infinite power, so too is "the ultimate height" (i.e., the progressive ascent and withdrawal of the Divine light in the direction of self-concealment [within its Source]) an expression of His infinite power.

And it is this self-obscuring ascent that is intended in the above-quoted statement [of Tikkunei Zohar]: "G‑d's infinite light extends upward without bounds."