It is an arc because it evokes the life cycle of a human being with a beginning, a middle and an end. The first stanza describes how daily routines and projects distract us from our own mortality. We keep ourselves busy to the point that we are able to forget it or at least not think about it. Such interpretation is confirmed by the second stanza were the narrator informs the reader that when she is taken by Death she was forced byt its inevitability to “put away her labor and her leisure”.
The fact that the third stanza speaks about a children school symbolizes the first stage in a person’s life, childhood. The fields of Gazing grain symbolize adulthood since if you follow the symbolism of the metaphor; human beings sow the seeds of their life during childhood and harvest them during adulthood and then the Sun sets, a clear symbolism of death, when the sun sets on a person’s life for the last time.
The end of such journey is the “house that seemed and dwelling of the ground” in other words, our tomb. However, this is not the end of our journey, only the end of our earthly life since the fifth stanza clearly allegorizes the continuation of the soul into “eternity”. Therefore, such arc is an arc of hope.