Reincarnation

A matter of cultural belief. I suppose what you come back as is a bit of a lottery. And is possibly based on what kind of life you lived prior to your departure. A concept offering hope to the masses and why not if it offers the prospects of a better life as a reward to the deserving and as a just punishment to those who were rats on two legs and come back as real four-legged ones.
Justice.
As for me, once around will be enough. As for what's on the other side - hey, if humans couldn't share this globe peacefully, why would they share Heaven any differently?