During the act of Creation, a residue of the lights of Tohu remained attached to the shattered vessels of Tohu, which became absorbed into the four worlds of Atzilut, Beriya, Yetzira and Asiya. What could not be absorbed into the realms of holiness became the vitality of the realms of impurity, known as "the impure kelipot". It is man's duty to elevate the 'sparks of holiness' from their fallen state…

It is man's duty to elevate the "sparks of holiness" from their fallen state. This process of extracting the sparks is called "Birur", meaning "clarification", which is part of a larger cosmic plan called "Tikun", meaning rectification or restoration of the broken vessels, and, consequently, the restoration of the proper cosmic order.

When the sparks of holiness are extracted from the kelipot and are rebuilt into the vessels of Tikun, the lights that formerly illuminated the sefirot of Tohu can once again be drawn down. But this time the repaired vessels will be able to contain the light.

Although in theory all the sparks from Tohu must be extracted from the kelipot and absorbed into holiness, practically speaking this cannot be done in the normal course of things. The kelipot are divided into two categories - kelipat noga and three completely impure kelipot. (Etz Chaim, shaar 49, ch. 2 ff.) Kelipat noga is an intermediate level between holiness and impurity, and the sparks that fell into it can be extracted through the proper observance of the mitzvot. The performance of most mitzvot requires the use of objects, the vitality of which stems from kelipat noga; some examples are wool from a sheep that is used to fulfill the mitzva of tzitzit, hide from a cow that is used for parchment on which Torah scrolls, tefillin and mezuzot are written, and the citron fruit and palm branch for the mitzva of lulav and etrog. The degree of holiness to which the sparks will ascend depends on the person's kavanot…

When a person performs a mitzva, the vitality of the object, and indeed the vitality of his own body, which also derives from kelipat noga, is elevated into holiness. The degree of holiness to which the sparks will ascend depends on the person's kavanot (sing. kavana - intention or mystical meditation during prayer or while fulfilling a mitzva).

The sparks that fell into the three impure kelipot, however, ascend to holiness only if a person who became involved with these kelipot (through sin) repents to such an extent that his deliberate transgressions become transformed into merits. (Rosh Hashana 29a) The consummation of this purification will be effected only in the future by G‑d Himself: "I will cause the spirit of impurity to pass from the earth" (Zachariah 13:22), and all the fallen sparks will be restored to holiness.