When a new disciple would come to the Ba’al Shem Tov, the first question he was asked was “what do you remember?” The Ba’al Shem Tov was jingling the deepest levels of the new disciple’s soul preparing him for the study of Chassidut. In the Arizal’s Kabbalah there was also “memory triggering” but it involved “recollecting” one’s previous incarnations, which of course do not reveal the soul’s existence as it was before the creation of the world, when it was still an actual part of G-d, the yechidah, the singularity aspect of the soul.
A well-known Chassidic story illustrates this point well:
After the Maggid of Mezheritch passed away (the Maggid was the Ba’al Shem Tov’s successor), the disciples each looked for a Rebbe to follow. The eldest of the disciples was Rebbe Menacham Nachum of Chernobyl. Rebbe Shneur Zalman, the founder of Chabad, did not follow his close friend Rebbe Nachum, but instead looked to Rebbe Menachem Mendel of Vitebsk for guidance. Rebbe Shneur Zalman and Rebbe Nachum would visit one another once a year on Sukot.
On one of those visits, when they were sitting and discussing the deep mysteries of the Torah in the sukah, Rebbe Nachum asked Rebbe Shneur Zalman: “Why did you take Rebbe Menachem Mendel as your Rebbe and not me?”
Rebbe Shneur Zalman replied: “I once saw him when he was giving audience and I realized that everything that the person seeking his council had done in his life was known to him.”
Rebbe Nachum shrugged as if to say that he too saw past actions.
Rebbe Shneur Zalman continued: “I then realized that not only could he see all his actions in this present lifetime, he also was aware of all of the person’s previous incarnations since the six days of creations.”
Rebbe Nachum shrugged again.
Finally, Rebbe Shneur Zalman said: “In the end I realized that not only could he see his past actions and past incarnations, he could also see everything that this soul was destined for in the future until the coming of the Mashiach and after.”
At that moment Rabbi Nachum raised his brows in wonder, thereby acknowledging Rabbi Shneur Zalman's choice of a Rebbe, but the conversation abruptly ended, as the Chassidim, who had been intently listening to the holy words of the two tzadikim from on top of the sukah, suddenly moved and were heard...
...from Inner.org, the writings of Rabbi Ginsburgh (hassidic kabbalist in Israel.