33. The principle of reincarnation is the natural consequence of the law of progress. Without reincarnation, how is it possible to explain the difference which exists between the present social state of the world and that of barbarous times? If souls have been created at the same time as bodies, those which are born today are all as new, all as primitive, as those who lived a thousand years ago. Let us add, that there is not between them any connection, no necessary relation; that they are completely independent of one another. Why, then, should the souls of today be better endowed by God than their predecessors? Why have they better comprehension, purer instincts, gentler manners? Why have they knowledge of certain things without having learned them? We defy anyone to dispute reincarnation without at least admitting that God created souls of diverse qualities, some superior to others, according to time and place - a proposition irreconcilable with sovereign justice (Chap. II, n° 19).
Say, to the contrary, that souls of today have already lived in remote times, that they have been barbarous as their age, but that have progressed; that to each new existence they carry the acquisition of anterior existences; that consequently the souls of civilized times are not which have been created superior, but which have perfected themselves with time, and will have the only plausible explanation of the cause of social progress. (“The Spirits’ Book,” Chaps. IV and V).
34. Some people think that the different existences of the soul are accomplished by going from world to world, and not in one same world where each Spirit appears only once.
This doctrine would be admissible if all the inhabitants of the Earth were on the same intellectual and moral level. They would then be able to progress only by going to another world, and their reincarnation on this Earth would be useless. Now God does nothing uselessly. One finds all degrees of intelligence and morality, from the wildness of the animal to that of the most civilized people; it offers a vast field to progress. One would ask why the savage should have to seek elsewhere the degree above him, when he can find it beside him, and soon, from stage to stage in this world of human progress? Why should he go to another world for stages of progress which he can find in this, as there are different degrees of advancement not only between nation and nation, but in the same nation and in the same family? If it were thus, God would have done a useless thing in placing ignorance and knowledge side by side, barbarism and civilization, good and evil, as neighbors; while it is precisely this contact which makes the backward ones advance.
There is then no more necessity for souls to change worlds at each reincarnation, than there is for a student to change colleges in going from class to class. Far from being an incentive to progress, it would retard it; for the spirit would be deprived of the examples offered him by those of superior degree, and of the possibility of repairing wrongs he has done in the same place, and in respect to the persons whom he has injured - a possibility which is for him the most powerful means for moral advancement. After a short cohabitation spirits would disperse, and become strangers to one another. The ties of family and friendship, not having time to consolidate, would be broken.
To the moral inconvenience, one would also add a material one. The nature of the elements, the organic laws, and the conditions of their existence vary according to their worlds. On this aspect there are no two that are perfectly identical. Our strivings in physics, chemistry, anatomy, medicine, botanic, etc. would serve no purpose in other worlds, although what we have learned is never lost. In addition to enhancing the intellect, the ideas acquired from such knowledge helps us to foster new concepts. (Chapter VI, from item n° 61 on). If the spirit were to make only one appearance, frequently of a short duration, in the same world, at every migration he would find himself in conditions entirely different. Each time there would be a new knowledge to acquire, and new forces according to laws unknown to him. All this, before he has the time to elaborate upon familiar elements; of studying them, or being able to exercise them. The constant changes would be an obstacle to progress. The spirit should, then, remain in the same world, until he has acquired in that world the sum of knowledge and the degree of perfection that such a world encompasses (n° 31).
That the spirits leave a world when they can acquire nothing more upon it for one more advanced, must be a truth, and is so without doubt. If they leave before having thoroughly graduated from one stage to another, it is without doubt, in individual cases which God weighs in his wisdom.
All has an object in creation, else God would neither be prudent nor wise. Now, if the Earth were the theatre for only one incarnation of each soul, of what use would it be for children who die in infancy to come to pass only a few months, sometimes hours, during which they acquire nothing? – the same of idiots and fools. A theory is only good when it solves all the questions it raises. The question of premature deaths has been a stumbling block for all doctrines, except for the Spiritist Doctrine, which alone solves it rationally.
For those to whom is furnished a normal career on Earth there is a real advantage when finding themselves again occupants of the same place in order to continue there something they have left undone, often in the same family, or in contact with the same persons, in order to repair the evil they have done, or to submit to the law of retaliation.