When we begin to experience the higher spiritual parts of our nature, we recognize that here there is soemthing which is clearly beyond the physical material manifestation and independent from it. We thus have found the basis for accepting conclusively the need for and the reality of rebirth. Our spiritual nature can adopt a standpoint which is able to observe and either give consent, or withhold consent, to the actions of the mind, life and body. This portion of our being, which we may designate the “soul”, is not limited by physical heredity or by the influence of environmental factors. We can observe, and even participate in, the evolutionary development of the soul.
Sri Aurobindo points out: “Quite apart from any evidence of an after life on other planes or any memory of past births, this is sufficient warrant for a refusal to accept as sufficient any theory of the ephemeral being of the individual and the sole truth of the evolutionary Universal. Certainly, the individual being is not thereby shown to be independent of the All-Soul; it may be nothing but a form of it in time. But it is sufficient for our purpose that it is a persistent soul form, not determined by the life of the body and ceasing with its dissolution, but persisting independently beyond. For if it is thus independent of the physical race continuity in the future, if it thus shows itself capable of determining its own future soul evolution in time, it must have had secretly such an independent existence all through and it must have been determining in reality, though no doubt by some other and indirect insistence, its past soul evolution too in time.”
It is possible that the individual soul is either a portion of the All-Soul, or independent of it. Either way, as long as there IS an independent individual soul that evolves through time, the process of rebirth becomes a given. “But it is sufficient for the theory of rebirth that a secret soul continuity of the individual does exist and not alone a brute succession of bodies informed by the All-Soul with a quite ephemeral illusion of mental or spiritual individuality.”