Death is the end of the life of most Creatures, whom possess mortality. When Death occurs one’s spirit is separated from one’s body, usually passing onto the River of Death - though it also may stick around to haunt as a type of Ghost. It is unknown what happens with a soul beyond the River.
People have throughout all of History both feared and revered death as the most inevitable thing in life. The rites around death are thus important to most cultures, such as burials and veneration of the dead and one’s ancestors.
There have always been those who have sought to delay, avoid, defy or return from death - such as Necromancers and Liches creating Undeath. Divine Magic magics in particular are also known to have powers over death, specifically the ability to return people who have only been dead for a short period, which is considered more acceptable than that of other necromancy.
The Utopian Promise is a supposedly secret promise by the Titans to ensure immortal life after death together with one’s deity in Haeven - or if you transgress them - a long payment to be paid in a hellish plane.