Classical Jewish philosophy explains that although G-d is good, and it is His nature to do good, He created the world with evil to give His creations an arena of free-choice to choose good over evil. This is necessary to enable His creations to earn the greatest possible goodness that G-d can bestow upon them, which is Himself. Hassidism emphasizes that the ultimate purpose of creation is to create a dwelling for G-d in this world by refining and elevating the body and its portion in the world. The presence of evil poses the greatest challenge in this quest, but the greater the darkness and the stronger the forces of evil, the brighter is the transformation of that darkness into brilliance. Kabbalah uses the term Kelipah to describe evil, and divides everything in this world into either Sitra D’Kedushah or Sitra Achra, meaning the side of holiness or the side of impurity. Kelipat Nogah can be uplifted, while Shalosh Kelipot Hatmayot are totally impure Kelipot.
The Tanya (Likutei Amarim) explains explains that anything that is not directed towards G-d and His will and service is considered sitra achra, or "the other side," and does not receive its vitality from the holiness of G-d. The world of kelipot and sitra achra is considered severe and evil, and wicked men prevail.
A completely righteous person has entirely divested themselves of evil, which has been converted to goodness, and hates the sitra achra (the evil inclination) with an absolute hatred.
The kelipot and sitra achra, which receive their life and existence from the Divine word and the breath of His blessed mouth in concealment of His Countenance, are called "other G-ds." The Supernal Will, of the quality of "Countenance," is the source of life which animates all worlds, but the sitra achra is not bestowed on it and even the so-called "hinder-part" of the Supernal Will is not actually clothed in it. The sitra achra constitutes actual idolatry and denial of the unity of the Supreme King of kings, since it surges upward like an eagle, saying, "I am, and there is nothing beside me."
The quality of the "Intermediates" and their service is to subdue the evil impulse and thought rising from the heart to the brain and to avert the mind completely from it. The sitra achra (evil inclination) is subdued through this action. There are two kinds of gratification before G-d: the complete annihilation of the sitra achra by the tzaddikim and when the sitra achra is subdued whilst it is still at its strongest and most powerful and soars like an eagle, which is accomplished by the Benonim. Sacrificing one's impulses to subdue the sitra achra is rewarded, and even the wicked man shall repent of his evil and turn his evil into "day" and light above, when the sitra achra is subdued.
The joy of the Lord and the gratification of rendering it by virtue of faith can subdue the darkness of kelipot and sitra achra in this corporeal world. Israel was given the Torah to help subdue the sitra achra, which opposes the Divine, and ultimately, the Messianic Era and the Resurrection of the Dead will fulfill the creation of the world.
The Tanya describes the three levels of contraction giving rise to the three comprehensive worlds of Beriah, Yetzirah, and Asiyah, each consisting of numerous particulars. The purpose of these contractions is to create the human body and subjugate the sitra achra, to bring about the preeminence of light over darkness.
The Tanya (Likutei Amarim) explains that anything that is not directed towards God and His will is considered the "other side" and does not receive its vitality from God. The world of evil is considered severe and wicked men prevail. A completely righteous person has entirely divested themselves of evil and hates the evil inclination with absolute hatred. The purpose of the contractions is to create the human body and subjugate the evil side, to bring about the preeminence of light over darkness. Israel was given the Torah to help subdue the evil inclination, and ultimately, the Messianic Era and the Resurrection of the Dead will fulfill the creation of the world.