The meaning of death. Ever since we were all little boys and little girls playing house, or showing each other our genitals in our parent's bedrooms, ever since we were first encountered with the idea that there is a finality, that life in all its glory is just a faint little echo in the tunnel of time, ever since we realized that life actually ENDS, we have become bitter, self-centered bastards who go on to become empowered members of society. We seem to want to leave a mark, to become immortal in a way by living on in the memories of those that are still living. We grow up. We find new ways to deal with death.
Religion is basically a philosophy centered on the idea of dealing with death.
Without death, there would be no religion. We can't accept the fact that when we die, we turn to ashes and disintegrate into fertilizer for weeds. So we make up fairy tales to trick each other into denial. Death will not get the last laugh. We are immortal.