It is a foolish hypothesis, but we may make use of it, to make things clear: let us think for once what might have arisen if you all were merely born of your parents. Let us leave Karma out of consideration, and leave out of account the fact that we are, of course, born into definite families; and let us only regard physical heredity. Then you would all be alike as human beings. You would only have the general human physical character. That you are quite definite individuals, that so many individual beings sit here before us, rests on the fact that the general human form, even in its finest principles, is fashioned by the spiritual individuality which descends from the spiritual world and enters into that which is given by father and mother.
To that end, just as we must have fingers to grip an object in the physical world, just as we must perceive an object in order to grasp it — even as we must have the necessary organs and also must have learnt to grasp a thing — so must we have learnt to attach ourselves to all the different organs which form our body physically. We have all got ears, but we each hear in our own way. We all have eyes, but we see individually. For the external organs this is least perceptible; in the inner behaviour of man it is more striking.
Thus we must insert our psychic-spiritual essence into all these quite general organs, and fashion them individually. We must learn to know the forces, the inner psychic-spiritual formations, so that what we receive through inheritance as ears, nose, eyes, brain, etc., we can fashion individually. That means that when at birth we enter the physical world we must have knowledge, and not only knowledge but practical possibilities of using it. This wonderful structure of man, how little do we really know of it through external science?
We must inwardly learn the whole subtle structure of the brain, because we have to organise it inwardly. And all these spiritual-psychic processes, everything which makes it at all possible for us to be men in a human body between birth and death, all this we have to acquire for ourselves. Just as we have to acquire abilities for ourselves in life, so we must also acquire between death and rebirth the power of being men in physical life. We must keep this in view.