Q. Kvod Horav I recently heard something that I found very disturbing. I was told that the 'Neshama Yeseira' or added soul that one acquires during Shabbat, can actually be the soul of another once living being such as a Tzadik or a forefather that comes to visit during the holy day. That sounded to me very strange and like being possessed by a strange soul. Could that be true?
A. I did first consult with a number of renowned Rabbonim and they also mentioned that it is a strange and likely false idea.
However, when I researched a bit I found that the idea is not strange at all in Cabbalah and Chasidus seforim.
Tiferes Shlomo (P. Bamidbor) mentions that when one performs a mitzva with great Kavanah, intention and Shleimus, he merits not only the help and of a Tzadik that performed this mitzva in a similar way, but his presence in him also.
Lebushei Aharon (ibid) describes that indeed for. that person, when Shabbos arrives on that week, the Neshomo Yeseiro that comes to him, is that departed Tzadik's soul from past generations.
Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit'a