We can understand what is meant by the heavenly treasure house in terms of a statement in Tikkunei Zohar:

"G‑d's infinite light extends upward without bounds and downward without end."

The latter phrase means that the revelation and diffusion of this light are utterly infinite.

Hence the name "Or ein Sof", which indicates [not merely a light that emanates from G‑d Who is infinite, but] that the light itself is infinite, because it resembles its Luminary.

This represents the unique quality of light, for though it is merely a ray [from a source] and not the essence [of the source], it nevertheless resembles its source.

Hence, since [G‑d's] essence is uncompounded and infinite, the light that resembles it is likewise infinite.

Now light of this kind would bring into being worlds and Sefiros without number or end, worlds utterly different [than those we know].

Their infinity not only in number but also in nature is implied in the [Kabbalistic] expression "Sefiros without end."

The Idra Zuta compares such a Sefirah to "a candle whose light is diffused to all sides and corners [and hence may appear to be many lights], but when you look at it in order to know it, you will find only one candle."

Because the light [of such a Sefirah] is essentially simple, it can find expression in a limitless multiplicity of diverse levels: its "light is diffused to all sides and corners."

In truth, however, there is only one candle; [i.e., the light is the multiple expression of an essential unity].

This is the unity spoken of in the statement, — "You are One, but not in the numerical sense."

Since G‑d is essentially one, He transcends numeration when He reveals Himself; He is essentially One, even though His revelation is multifaceted.

[In view of this apparent multiplicity,] why did exactly ten Sefiros emanate from Above?

"Ten Sefiros," declares Sefer Yetzirah; "ten and not nine, ten and not eleven."

This state was brought about by the [self-limiting, self-screening] tzimtzum of the infinite light.

Thanks to it, G‑d's infinite light and revelation appear in finite categories.

Accordingly, the Sefiros are ten in number.

Nevertheless, even after the tzimtzum, unbounded and numberless worlds have come into existence.

A hint of this may be found in the verse, — "And maidens without number."

Said the Sages: "Do not read alamot (maidens), but olamot (worlds)," for there are worlds without number.

In Idra Rabbah we likewise read: "At [the Supernal level that is termed] `the skull' there are 12,000 worlds."

This number is appropriate to the specific concept discussed there.

In fact, however, the worlds are numberless.

Even the lowest level of the World of Atzilus, namely, Malchus, gives rise to creation of innumerable multiplicity, as it is written, --"How manifold are Your works!"

Or, in another verse, --"How great are Your works!"

This multitude of creations and greatness of creations are discussed in the maamar beginning Vaeira.

All this is possible because the light is infinite; hence, in spite of the tzimtzum, it gives rise to an infinite multiplicity of creations.