Sri Aurobindo raises the consequential questions about the process of rebirth and the implications of the process. In previous chapters we reviewed the necessity of rebirth as part of the evolution of consciousness manifesting successively over time in the material world. We also concluded that there is a soul or psychic entity around which the successive evolutionary development coalesces through these successive births. We now come to the question of the process of rebirth, how it relates to the question of other worlds or planes, and the process of the spiritual evolution itself. Sri Aurobindo explains the issues that need to be reviewed and addressed as follows: “if that process is not quickly successive, birth immediately following death of the body so as to maintain an uninterrupted series of lives of the same person, if there are intervals, that in its turn raises the question of the principle and process of the passage to other worlds, which must be the scene of these intervals, and the return to earth-life. A third question is the process of the spiritual evolution itself and the mutations which the soul undergoes in its passage from birth to birth through the stages of its adventure.”
The crux of the issue is that unless there is immediate succession, the soul must exist somewhere, in some world or state, in some form, during the time between the one event and the other; and assuming then that it resides in some other world or plane during that time, there must be a mechanism of its movement out and back again into the physical world. This also gets into the question of what the soul carries with it from the past lifetime, if anything, and what it brings with it into the next lifetime, if anything. This brings us to the question of the process of the spiritual evolution.
Sri Aurobindo, The Life Divine, Book 2, Part 2, Chapter 22, Rebirth and Other Worlds; Karma, the Soul and Immortality