This world alone, the physical world is not. This is ancient Vedic knowledge that there are many planes of existence. There is vital, mental plane and there are higher planes such as Satchitananda plane. In fact the Veda speaks of the seven planes of existence, the Sat plane, the Chit plane, the Ananda plane, the Truth plane, the Mind plane, the Life plane and the Physical plane. This is idea of the saptarashmi – seven rays. The Veda says all the seven are interconnected and interwoven. And wherever we look around the world all the seven are present, although all the seven may not be dominant, may not be manifest very clearly. So when the vital being leaves the body along with the soul and mind, it transmigrates to the life plane. This is the reason why Kathopnishad says, Yama tells Nachiketas, one who believes that this world alone is and there are no other worlds he can never be liberated because he is constantly attached to the physical world. So once you go to the life plane then you get a freer domain of expressing your vital being. This also is a very important idea.
What does it mean to get a freer field to express the vital being? You notice that in this world of the physical, we are constantly hampered by physical disabilities. There are many things that we would like to do but either we are sick or we get fatigued very easily, or else there is a need for sleep. Very often when our vital being is very powerful we feel we should have 48 hours in a day to be able to do everything that we want to do. There are so many things to be done but it is the physical existence which hampers our full manifestation of all our vital activities. In the vital plane this disability would not be there, so that it may have a freer play of its energies. Very often many things that we cannot do here in the physical plane we are able to accomplish in the vital plane, this we are able to do by transmigrating into the life plane. And we reach a point where all that we wanted to do is as it were exhausted.
Once that is done then we are able to pass to the other plane and if our mind was developed to some extent then we go to the mental plane. There again, what we were not able to do mentally here, we are able to accomplish over there. And a point is reached where it is exhausted and then we are able to move to the plane of the pure soul being which is called the Psychic plane. It is the psychic being actually, which is the individual formation of the soul; which is immortal, it never disintegrates, it is the inextinguishable flame. So that which really survives the body after the death of the body it is this psychic body or soul which remains disintegrated. The vital can become exhausted, mental can become exhausted but the soul is never exhausted. It is actually you might say an entity of potentiality which remains disintegrated.
It is this soul personality which has a sojourn on the psychic plane. And according to the level of evolution that it has reached in the past births, and according to the potentiality it has got of manifestation in the future, it waits for the circumstances on the earth to arise appropriate to the need and then it takes a new body on the physical plane by descending into the physical plane. Very often when the soul is not very developed it does not make a conscious choice of the circumstances in which it is to be born. It happens almost like gravitation. But when the soul development has been sufficiently great, then it can decide exactly when it is to be born. It can even preside over the formation of the body, determine the formation of the body and take the birth according to its needs very consciously. In the case of very developed souls this is the normal condition. So it is actually the soul that takes birth.
One who is reborn is the soul that is reborn, and while taking rebirth it may have discarded the previous personalities altogether because they are no more necessary for future growth and future potentialities to develop. Or it may take help of whatever was formed and enter into the new body with all the formations of the past birth in whatever way they are modified, after going into those planes by going through necessary modifications with enriched material derived from the experiences of those planes. As a result of that we cannot expect that the soul that is now born will manifest the same tendencies which were present in the last incarnation. Napoleon of the last birth may be in this birth an ordinary soldier, no more the captain of the commander. Or he may be a businessman in the next birth or an ordinary navigator, depending upon what experiences he had already exhausted and what new potentialities he has to manifest. So it is idle to expect in a new personality continuation in the same form or same rhythm as it was in the previous birth.
The common notion that the same personality who dies now is reborn is quite unscientific. It is only true of those very rudimentary personalities which have no capacity of transmigrating to higher planes and to exhaust themselves and to renew themselves, it is true only of those personalities. But for the others it is not so for most of the human beings it is not so. Otherwise there would be no evolution. If you are simply to be born again into a new body it would be senseless. Why would you have left the earlier body at all? We leave the earlier body because the circumstances in which we are living, the capacities which are there in the body have reached their point where they cannot have further development. We have reached a critical point where continuing in the same body has no further meaning in terms of evolution.