Kabbalists attained spirituality and wrote about it in their books. They perceived that the root of the entire reality is a Supreme Power, which they named “His Essence”, because they could not attain the power itself. However, they did perceive that there is a thought, an aim, to create creatures in order to delight, which comes from His Essence. They named that thought and aim “The Thought of Creation”, or “Upper Light.” It turns out that from the creature's perspective, the Light is the Creator, because it cannot attain His Essence. Hence the Creator-creature contact is maintained through the Upper Light.
In short, there is a Light that stems from His Essence. The Light wants to create a creature and delight it by filling it with pleasure. That is, the purpose of the Light is to create a creature that would feel the Light as pleasure.
The Kabbalists therefore called the creature “vessel” and the Light “filling.” The Light that stems from His Essence in order to create the creature is called Behinat Shoresh (Root Phase), because it is the root of the entire reality. That Light then creates a desire to take pleasure in the Light. The desire for pleasure is also called “Will to Receive” (Light).
The intensity of the pleasure depends only on the intensity of the desire to receive it, just as in our world one may have an empty stomach, but no desire to eat. Hence, the desire is the vessel for the filling, and without it there is no pleasure. There is no coercion in spirituality and the filling is only equal to the desire.
The Light that stems from His Essence creates a vessel and fills it. The pleasure that the creature feels when it receives the Light is called Ohr Hochma (Light of Wisdom). The desire created by the Light that fills it is called Behina Aleph (First Phase). It is called by that name because it is the first Behina (appearance/manifestation) of the future vessel. But that desire is not yet an independent one, as it is created directly by the Light.
The actual creature is the one whose desire to enjoy the Creator's full Light for its own delight. This desire and the decision to enjoy it for self arise from within. Such desire needs to be imprinted in it by the Creator.
In order to receive Light, the creature must know how intense the pleasure from the Light is before it receives it. Then, it must be filled with Light, and then feel what it is like to be without the Light. Only then is the real desire for the Light created.
In much the same it happens in our own lives, when a person is given a new fruit to taste, there is no preliminary desire for it. But if one tastes it and feels the pleasure in it, and the fruit is then taken away, the person begins to crave it and wishes to bring back the pleasure. It is precisely that desire, the new desire born in man, that is what man feels as an independent will.
Hence, it is impossible to build the vessel all at once. In order for the desire to know what to delight in, and recognize its own desire to enjoy, the desire must go through the entire chain of events. That condition is presented as a law in Kabbalah: “The expansion of the Light and its departure, make the vessel worthy of its task,” which is to receive Light and enjoy it. The phases of the evolution of this desire are called Behinot (phases/distinctions/observations) because they are phases in the building of discernments/observations in the will to receive.
Thus, along with the pleasure, the Light renders the vessel with the attribute of bestowal. And the vessel suddenly discovers while enjoying the Light that it wants to give, just like the nature of the Light that fills it. This is because the Creator purposely rendered the Light with the ability to convey its own attributes along with the desire to bestow. Once the Light fills up the vessel in the first phase, the vessel feels that it want to be like the Creator. And because this is an entirely new desire, it is an entirely new observation, named Behina Bet (Second Phase).
Behina Bet is a desire to give. The pleasure it feels at resembling the Creator is called "the Light of Mercy." Thus we see that Behina Aleph is opposite to Behina Bet because the desire of Behina Aleph is the will to receive, whereas that of Behina Bet is the will to bestow. The Light in Behina Aleph is a "Light of Wisdom," and that of Behina Bet is a "Light of Mercy."
When the will to receive in Behina Aleph begins to enjoy the Light that fills it, it immediately feels that the Light is the giver of the pleasure and that the will to receiver of the pleasure, and thus begins to want to be like the Light itself. Rather than receive the pleasure, there is a desire to give it, like the Light.
Hence, the original will to receive leaves, and the vessel remains empty of the Light of Wisdom, because pleasure can be felt only when there is a desire for it.
The will to receive cannot remain without the Light of Wisdom, because the Light of Wisdom is its livelihood. Therefore, this will to receive must take in a little bit of the Light of Wisdom. Thus, this new desire, called Behina Gimel (Third Phase) consists of two desires:
The vessel now feels two Lights: the Light of Mercy in the will to bestow, and the Light of Wisdom in the will to receive.
When Behina Gimel receives Light, it finds that between the Light of Wisdom and the Light of Life, the former is more consistent with its nature. It then decides to receive this Light fully. Thus an independent desire to receive the Light of Wisdom, and the very desire with which the Creator wants to fill the creature is now created.
We see that the Light that emanates from His essence creates a vessel in four steps. That is why that final desire, named Behina Dalet (Fourth Phase), is in fact the only creature. All the phases that preceded it were only phases in its evolution. In fact, the entire Creation is comprised of that fourth phase. Everything that exists, except for the Creator, is that Behina Dalet. This Behina Dalet is named Malchut (Kingship), because the will to receive governs it.
Four Phases
The fourth phase is the only creature. It is divided into outer parts and inner parts. The outer consists of Sefirot, Partzufim, worlds, and our world, and the still, vegetative and animate. The inner part consists of the human souls. The difference between those parts is only in the magnitude of their will to receive.
When the fourth phase is entirely filled with Light of Wisdom, it is called Olam Ein Sof (World Without End), because its desire doesn’t limit the reception of the Light. The fourth phase receives through the four prior phases: Root, First, Second, and Third. It turns out that the fourth phase is divided into five parts (including its own phase) of will to receive.
Summary
Light comes from the Creator, or the Root Phase. The Light then creates a creature, the fourth phase, in four phases. The essence of the creature is the desire to receive pleasure. The pleasure is the sensation of the Light within the desire. The fourth phase is then divided into four inner parts, which receive Light from the four preliminary phases. The fourth phase, filled with Light of Wisdom, is called the "World of Ein Sof" (no end). The parts of the fourth phase are called "souls" and "worlds." The worlds contain Partzufim, Sefirot and everything that is not souls.