By Rabbi Shneur Zalman of Liadi The Alter RebbeTo Understand the Concept of the Tzimtzum 5565-1805 Indented text by the translator

                                         Stop Light                                                    

LIGHT HEAD

The Tree of Life describes the great withdrawal and contraction (tzimtzum harishon) which concealed God’s Infinite Light (ohr ein sof). How can we understand this concept?
The Essence of the Godhead is in a state of absolute simplicity, beyond any manner of description. God desired to emanate 10 attributes (sefirot). These emanations, though, are completely unrelated in value to His Essence. Indeed, it was impossible to effect their emanation from His Essence—called the essential Light-source.

The Alter Rebbe employs two terms to describe God’s Essence: Godhead and Light-source. For our purposes, the terms are interchangeable. Likewise two terms are used for that which was ultimately emanated: emanations and light.
These terms are better understood in Hebrew. Godhead refers to the m’atzil—that which emanates. Emanations themselves are called n’atzalim. The Light-source is termed m’ohr—that which emits light. Light itself is known as ohr.
The world of Emanation (atzilut) refers to the final, rectified state of emanation. Its 10 sefirot were emanated from a specific Godhead, which serves as their source. Primordial worlds exist above the world of Emanation. Their sefirot were likewise emanated from their specific Godheads.
The subject of the Alter Rebbe’s discourse is the ultimate Godhead—the Essence of God’s Being. He thus employs the phrase “Absolute Essence of the Godhead and Light-source.”

LIMITLESS LIGHT

The ultimate Light-source may or may not illuminate. To initiate the creation process, God first had to shine light out from Himself.

Since the Absolute Essence of God can’t be the source of creation, how did it start? First God had to radiate a mere ray out from Himself. That radiated light (the Infinite Light) ultimately brought the four worlds of Emanation, Creation, Formation, and Action into existence.
This revelation of Infinite Light is called Kingship of the Infinite One (Ein Sof). More precisely, this light is the radiance of the Name of His revered Kingship (malchut). All the worlds would ultimately be brought into existence from this radiated light.

The Infinite One also refers to God’s Essence. For this reason, Kabbalah calls the Infinite Light ohr ein sof. The withdrawal still hasn’t occurred. Above (prior to) the withdrawal exists the realm of Ein Sof. There, quasi attributes are expressed in God Himself. The lowest is called Kingship.

EARTH KING

A king of flesh and blood who rules over many nations illustrates this concept. His personal attribute of Kingship isn’t associated with the essence of his soul. This is dissimilar to his other spiritual attributes, which are part and parcel of his essence; they affect the essence of his soul in a profound manner.
For example, when a king rages in anger, his soul’s essence is aroused. All his limbs shake and blood races through his veins, reddening his face. His physical appearance is dramatically altered due to the arousal of his soul’s essence. His attribute of Loving Kindness likewise affects the soul’s essence. So does his attribute of Victory, and every one of his other attributes. This is due to the fact that all his spiritual attributes, with the exception of Kingship, are considered essences. They derive from the essence of his being.
Kingship, on the other hand, is merely a radiance projected to others. Its purpose is to establish his exaltedness, which enables him to rule over other people. Kingship influences people to call him “king.” Rather than expressing his soul’s essence, Kingship is merely a spiritual radiation. His royal name spreads out among the masses. Thus, this radiated name isn’t linked to the essence of the king’s soul. Unlike his other attributes, it doesn’t affect his absolute being.

SKY KING

The example of a corporal king allegorizes the condition of God’s Essential Being. The pristine state of Light-source cannot bring worlds into existence. Rather, only a mere radiation—God’s Infinite Light—can create them. His light spreads outward in order that all the worlds will be called by His royal Name—Kingship of the Infinite Light.
However, the 10 sefirot of the world of Emanation still couldn’t be emanated from this Infinite Light. It was first necessary for God to withdraw His light. That would in turn create a vacuum. Then God could project a solitary light beam straight into the void. The 10 sefirot could then emanate from this beam.

                                                           References   

LIGHT HEAD

the great withdrawal and contraction (tzimtzum harishon)
Eitz Chaim, portal 1, section 2.

contraction (tzimtzum
Midrash Tanchuma, parshat Vayakel, chapter 1.

The Essence of the Godhead is in a state of absolute simplicity, beyond any
Tikunei Zohar, chapter 69, page 115, side b;
Maimonides, Mishnah Torah, Hilchot Yesodei HaTorah, chapter 1, law 7;

God desired to emanate 10 attributes (sefirot).
The First Book of the Zohar, page 29, side a;
Pardess Rimmonim, portal 11, chapter 5.

Godhead refers to the m’atzil—that which emanates.
Pardess Rimmonim, portal 16, chapter 1.

Its 10 sefirot were emanated from a specific Godhead … their source.
Avodat HaKodesh, volume 1, chapter 2;
Pardess Rimmonim, portal 3, section 1.

Primordial worlds exist above the world of Emanation.
Eitz Chaim, portal 6, chapter 1; ibid., portal 7, chapter 1; ibid..

LIMITLESS LIGHT

The ultimate Light-source may or may not illuminate light.
Shelah, Toldos Adam, chapter Beis Israel, introduction.

This revelation of Infinite Light is called Kingship of the Infinite One (Ein Sof).
Tikunei Zohar, introduction, page 13, side a.

this light is the radiance of the Name of His revered Kingship (malchut)
The Second Book of the Zohar, page 134, side a.

The Infinite One also refers to God’s Essence.
Pardess Rimmonim, portal 11, chapter 5.

There, quasi attributes are expressed in God Himself.
Sifra, parshat Acharei Mos, chapter 8, paragraph 1;
The Third Book of the Zohar, page 65, side a;
Midrash Tehilim, chapter 50, verse 1.

SKY KING

Rather, only a mere radiation—God’s Infinite Light—can create them.
Tanya, Igeret HaKodesh, chapter 20, page 131, side b.

His light spreads outward in order that all the worlds will be called by His
The Book of Psalms, chapter 148, verse 13.

His royal Name—Kingship
Pri Eitz Chaim, portal 7, chapter 9.

Then God could project a solitary light beam straight into the void.
Eitz Chaim, portal 1, section 2.