Wheat that has put forth its grain is mature. In this metaphor, birth is dawn, maturity is noon, old age is twilight, the moment of death is sunset, and the state of death is night. In our conventional schema for a day, as the sun sets, the dew and chill set in. Metaphorically, death's coldness is night's coldness, since death is night. We conceive of death as something to which we are all subject.
Death is inevitable and final.
But since one inevitably dies, so the metaphorical departure is inevitable, as is the final state to which it leads. Being dead is a final state, and therefore, metaphorically, a final location. A change of state is metaphorically a change of location. If one conceives of the earth as where the body comes from and returns to and belongs, then one can conceive of the grave as the home, not just the house, of the body. Bible, Genesis Home is where you start from and return to, and it is where you belong.