36. At certain epochs regulated by divine wisdom, these emigrations and immigrations take place en masse in consequence of great revolutions, causing great numbers of human beings to change worlds, which are soon replaced by equivalent incarnations. It is then necessary to consider destructive scourges and cataclysms as collective arrival and departures - providential means of renewing the material population of the globe by replenishing it by the introduction of new and purer spiritual elements. If in these catastrophes there is a great destruction of bodies, they are only torn vestments; but no spirit perishes. They only change place. Instead of departing alone, they go in numbers, which is the whole difference from the ordinary. By one cause or another they must inevitably depart sooner or later.
The rapid and almost instantaneous renovations which take place in the spiritual element of the population, in consequence of destructive scourges, hasten social progress. Without emigrations and immigrations, which from time to time give a violent impulsion, it would march very slowly.
It is remarkable that all great calamities which decimate populations are always followed by an era of marked spiritual, intellectual and physical progress in the social state of the nations in which they occur. Their object is to produce a great change in the spiritual, which is the normal and active, population of the globe.