Personification occurs in five instances in "A Psalm of Life." In each case, Longfellow uses personification to enhance the imagery of the language and emphasize the depth of emotions in particular lines.
The subtitle of the poem sets up the speaker as the personified "Heart Of The Young Man" in order to stress the passion of the dramatic monologue that will follow. As an archetype, a "Young Man" is a passionate, heroic figure. Therefore, by additionally personifying a "Heart," typically a symbol of strong emotion, the poem doubly stresses the passions of the speaker.
In line 4, the "soul" is also personified as a figure that can live and die: "For the soul is dead that slumbers." Specifically, a sleeping soul is a "dead" one, numb to the experiences of life. Therefore, an individual can gravely harm their soul by passively experiencing, or "slumber[ing]," through life. Consequently, by personifying the soul as a figure that can be harmed or even killed, the speaker heightens the danger of not living in the present.
In line 6 and 7, the speaker also personifies "Life" as a figure with "goal[s]." The "grave," the speaker makes clear, is not a "goal" of life. Rather, life has other goals and deserves the full attention of those who can experience it. One must, the speaker suggests, live life fully in the present. Personification, therefore, stresses the importance and reality of "Life."
In line 15, the speaker again personifies "hearts," now as individuals that are "stout and brave." This further develops the personification of the "Heart Of The Young Man" in the subtitle. By providing hearts with positive character traits of strength and courage, the speaker treats hearts as heroic figures. This personification emphasizes the importance of hearts in individual lives and, particularly, of living with sincerity and emotional depth. At the same time, though, the reader reminded is reminded that hearts "are beating / Funeral marches to the grave." Eventually, all hearts stop beating. Death plays an important role in human attitudes towards life.
In line 23, the "Past" is personified and figuratively brought to life as a figure that is able to "bury its dead." At the same time, the "Past" is described as a "dead Past." Through personification, the speaker acknowledges the powerful presence of the "Past" as similar to a living figure. However, simultaneously, the speaker makes clear the necessity for his audience to let go of the past and move on. As in the previous instances, personification enhances the vivid imagery of the lines while heightening the emotions behind them.