A soul that returns to the world through reincarnation does not necessarily return with the same Self as before.
The Self is not a function of the soul alone.
It depends on the connections between the soul and the body, and between both of these and the environment, as well as the time and place in which that soul is living.
has a new body and new flesh-and-blood parents, and it lives in a different place at a different time than the previous incarnation.
All these factors create a Self that is different from the original one, despite the fact that it is the very same soul as before.
The entrance of the reincarnated soul into a new body therefore means a new beginning and a new life experience for it.
–Rabbi Adin Steinsaltz