The following is an excerpt from “The Life Divine”, by Sri Aurobindo.
Our first conclusion on the subject of reincarnation has been that the rebirth of the soul in successive terrestrial bodies is an inevitable consequence of the original significance and process of the manifestation In earth-nature; but this conclusion leads to farther problems and farther results which it is necessary to elucidate. There arises first the question of the process of rebirth, 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.
If the physical universe were the sole manifested world, or if it were a quite separate world, rebirth as a part of the evolutionary process would be confined to a constant succession of direct transmigrations from one body to another; death would be immediately followed by a new birth without any possibility of an interval, – the passage of the soul would be a spiritual circumstance in the uninterrupted series of a compulsory, mechanical, material procedure. The soul would have no freedom from Matter; it would be perpetually bound to its instrument, the body, and dependent on it for the continuity of its manifested existence. But we have found that there is a life on other planes after death and before the subsequent rebirth, a life consequent on the old and preparatory of the new stage of terrestrial existence. Other planes co-exist with ours, are part of one complex system and act constantly upon the physical which is their own final and lowest term, receive its reactions, admit a secret communication and commerce. Man can become conscious of these planes, can even in certain states project his conscious being into them, partly in life, presumably therefore with a full completeness after the dissolution of the body. Such a possibility of projection into other worlds or planes of being becomes then sufficiently actual to necessitate practically its own realisation, immediately and perhaps invariably following on human earth-life if man is from the beginning endowed with such a power of self-transference, eventual if he only arrives at it by a gradual progression. For it is possible that at the beginning he would not be sufficiently developed to carry on his life or his mind into larger Life-worlds or Mind-worlds and would be compelled to accept an immediate transmigration from one earthly body to another as his only present possibility of persistence.
The necessity for an interregnum between birth and birth and a passage to other worlds arises from a double cause: there is an attraction of the other planes for the mental and the vital being in man’s composite nature due to their affinity with these levels, and there is the utility or even the need of an interval for assimilation of the completed life-experience, a working out of what has to be discarded, a preparation for the new embodiment and the new terrestrial experience. But this need of a period of assimilation and this attraction of other worlds for kindred parts of our being may become effective only when the mental and vital individuality has been sufficiently developed in the half-animal physical man; until then they might not exist or might not be active: the life experiences would be too simple and elementary to need assimilation and the natural being too crude to be capable of a complex assimilative process; the higher parts would not be sufficiently developed to lift themselves to higher planes of existence. There can be, then, in the absence of such connections with other worlds, a theory of rebirth which admits only of a constant transmigration; here the existence of other worlds and the sojourn of the soul in other planes are not an actual or at any stage a necessary part of the system. There can be another theory in which this passage is the obligatory rule for all and there is no immediate rebirth; the soul needs an interval of preparation for the new incarnation and new experience. A compromise between the two theories is also possible; the transmigration may be the first rule prevailing while the soul is yet unripe for a higher world-existence; the passage to other planes would be the subsequent law. There may even be a third stage, as is sometimes suggested, in which the soul is so powerfully developed, its natural parts so spiritually alive that it needs no interval, but can immediately resume birth for a more rapid evolution without the retardation of a period of intermittence.