“ A culture believes that souls are recycled. One child gets half of a soul, another child gets the other half. However, this means that with each passing generation, the amount of soul in the child will become less and less (Through division)until their culture will die in the future because of their soulless offspring.”
“ When you sleep, your soul briefly returns to the place where it was created/goes to when it dies, and seeks nourishment. Everybody's soul is created with a little link (or you could say a greater entity calls it back) to that place so that it can return easily, but upon death, the soul returns via that and annihilates the link as if returns.
Also, as an added thingy, you could say the entity supplying the link, or residue of the links themselves, (whichever) is the source of all arcane power.”