But in Kabbalah, Jewish mysticism, it's a fundamental idea, especially when we talk about the creation of the universe.

Before anything existed, there was only Eyn Sof, the Unlimited. Think of it as pure, boundless, perfect light. The Kalach Pitchei Chokhmah, a key Kabbalistic text, tells us that as long as the Unlimited was all there was, everything was, well, completely perfect. No imperfections, no needs, just pure being.

But then, something happened. A withdrawal, a contraction, known as Tzimtzum. The Unlimited, in a sense, "departed," making room for creation. This is where Malchut, often translated as "Kingdom" or "Kingship," comes into play. Malchut is understood as a "container," a vessel ready to receive.

Here's the twist: Initially, this container wasn't filled with all the worlds we know. Instead, it was like an empty space. Now, was it completely empty? No. The Reshimu, the "Residue" or "Remnant" of the original light, was still present. Think of it like the faintest echo, the subtlest potential of everything that was to come. The Reshimu was like air—present but not discernible, not yet formed into the worlds.

So, even though the container was full of this ethereal "air," it’s still considered "hollow" in relation to Eyn Sof. How can that be? Because before the Tzimtzum, there was no need for anything more. Everything was already perfect. And even after the Tzimtzum, the encompassing Eyn Sof itself still lacks nothing! That which is still in need of perfection, still yearning to be filled, that is what we call "hollow"—lacking, that is, in relation to the absolute perfection of Eyn Sof.

Here's where it gets even more interesting. After this "hollow" space was created, a "Line" of light descended, transforming the Reshimu into the Sefirot. The Sefirot (singular: Sefirah) are the ten emanations or attributes through which the divine reveals itself and creates the world. This is what the Kabbalists mean when they say the Line "filled" the hollow.

As the Etz Chayim (Tree of Life) explains, this entire hollow space was then filled with the ten Sefirot of Adam Kadmon, the primordial human. Adam Kadmon isn't a physical being, but rather a spiritual archetype, the first configuration of divine light structured in a human-like form.

So what does all this mean for us? Perhaps it’s a reminder that even in our perceived emptiness, even in the "hollow" spaces of our lives, there is always the potential for divine light, for the Sefirot to manifest. Maybe our imperfections, our yearnings, are not flaws, but rather the very spaces where the divine seeks to fill us with wholeness. It’s a powerful thought, isn't it?