Other religious traditions, such as ancient Egyptian, also conceive of death as a departure on a journey. I first surmised the Horses' Heads Were toward Eternity. In this poem, Death is taking the speaker on a journey, and the first part of the journey reviews the stages of life that one traverses during life's journey. The answer, in part, is that we know unconsciously and automatically many basic metaphors for understanding life, and Dickinson relies on our knowledge of these metaphors to lead us to connect the sequence she gives to the sequence of life-stages. Let us see how each of these metaphors works in detail.
Death comes with the harvest and the falling of the leaves.
The stages of the plants and parts of plants in their yearly cycle correspond to the stages of life. 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.