About Gilgul Neshamot
Transmigration of Souls
Gilgul Neshamot (Transmigration of Souls), in Kabbalistic teachings, is that the destiny of every soul is to return to the source where it came. Those who in their earthly existence failed to develop that purity and perfection necessary for gaining access to their heavenly source above must undergo incarnation in another body, and even repeat that experience more than once until they are permitted to return to the celestial region in a purified form.
The Zohar describes the incarnation of the soul in the following manner....From the beginning, G-d created all the souls in the very form in which they would afterwards appear in this world... At the time when the soul is to descend, Hashem calls it and says: "Go to such and such a place." The submits and descends against its will... If it returns laden with sin, it must obtain purification so as not to be delivered to Gehinnom... To be saved from punishment, the soul migrates from body to body.
In the opinion of most Kabbalists, no soul migrates through more than three bodies before it has run its entire course. The sinner expiates his sin in this world in the new existence in which his soul reappears. It may enter the body of a pious man, and by his good deeds he may cleanse the dross still adhering to the soul and facilitate its ascent on high. If pious men suffer, it is only and solely for sins committed in a previous existence; so that suffering is not a punishment for sins now committed, but a "purgatory" for evil deeds of a former life. On the other hand, the sinner may benefit from the good deeds that he performed in his previous existence. He prospers now, so that all his reward is eaten up by him in this world, and nothing but punishment is reserved for him in the hereafter.
Nachmanides (Ramban) in his commentary to the Book of Iyov (to Iyov 33:40) speaks of gilgul neshamot as a great mystery and the key to an understanding of many Scriptural passages.
Several characters of the Scriptures are said to be known to have transmigrated...the soul of Kayin (Cain) (Bereishit 4:1-16) entered the body of Yitro (Jethro) and the soul of Hevel (Abel) the body of Moshe. When Moshe and Yitro met in friendship they rectified the sin caused by the estrangement of the two brothers (Shemot 18:1-12).
Manasseh ben Israel (d. 1657) devotes a large portion of his Nishmat Chayyim ("The Soul of LIfe") to a defense of gilgul neshamot. In chapter 21, Manasseh observes that the doctrine was originally taught to Adam but was later forgotten. It was revived by Pythagoras, who was a Jew, and he was taught the doctrine by the prophet Yechezkel (Ezekiel). The Chasidim believe explicitly in the doctrine and tales are told of Chasidic masters who remembered their activities in a previous incarnation.