If the physical world is the cause and mechanism of existence, with no further significance or higher development, the question of rebirth is unnecessary. Similarly, if there is an “all-soul” that develops without regard to the individual development specifically, rebirth is also unnecessary. In order to have a significance to the concept of rebirth, there must be some type of individual soul that evolves and develops, and thereby needs and utilizes the process of rebirth. The existence of an individual soul does not imply that rebirth actually takes place as there are other possible explanations, but without an individual soul, there is no sense in a process involving rebirth.
Sri Aurobindo addresses these questions: “Now the question of rebirth turns almost entirely upon the one fundamental question of the past of the individual being and its future. If the creation of the whole nature is to be credited to the physical birth, then the body, life and soul of the individual are only a continuation of the body, life and soul of his ancestry, and there is no room anywhere for soul rebirth. The individual man has no past being independent of them and can have no independent future; he can prolong himself in his progeny…but there is no other rebirth for him. No continued stream of individuality presided over by any mental or spiritual person victoriously survives the dissolution of the body. On the other hand, if there is any element in us, still more the most important of all, which cannot be so accounted for, but presupposes a past or admits a future evolution other than that of the race mind and the physical ancestry, then some kind of soul birth becomes a logical necessity.”