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).