In Longfellow's poem "A Psalm of Life," the author uses symbols to refer to the various facets of life.
The third stanza symbolizes life's journey. Longfellow is telling his reader that the goal of each day is not finding one's way to joy or sadness, but to have made forward progress in the journey: to be farther along today than yesterday. This represents a sense of action, of forward movement.
Not enjoyment, and not sorrow,
Is our destined end or way;
But to act, that each to-morrow
Find us farther than to-day. (9-12)
The rhythmic marching of drums is symbolic not only of the passing of time, marking measured time to the end of our days on earth, but also of the seriousness of the task that lies before us. A drum was muffled during funerals, particularly for fallen soldiers. "Muffled drums" lends itself to the sense of solemnity. In this poem, the author refers to making certain we use life wisely to realize "noble and virtuous" achievements that will benefit others even after we have died.
Still, like muffled drums, are beating
Funeral marches to the grave. (15-16)
The next stanza carries on the military theme.
In the world’s broad field of battle,
In the bivouac of Life,
Be not like dumb, driven cattle!
Be a hero in the strife! (17-20)
A bivouac is an improvised military encampment. This section symbolizes the battles in which we are engaged during our lifetime. Once more the symbolism is somber. This is not simply a skirmish, but rather a battlefield that encompasses the world and all that is in it—anything and everything that might take us down. The shelter (bivouac) is temporary in nature, supporting the theme of life as a transitory existence. (This echoes the poem's theme of the swift passage of time.) The last military reference is the call to be a hero in the battle: to do something that rises above the casual or mundane. The use of military elements is symbolic of the battles we may often face in life. What we must endure, however, is not the most important element of the battle alluded to here. (It is found later as the reader is encouraged to take action to bring about tremendous feats of service.)
"Dumb, driven cattle" (line 19) symbolizes those who move through life without thought or direction. Cattle can be herded not only by horses, which can be intimidating, but also by dogs. The author warns the reader to be on guard against being led by others, as easily as a dog can direct a steer. Rather than being manipulated, the reader should avoid passivity and strive for something greater than those things people lacking vision cannot imagine.
The following stanza symbolizes situations and experiences in life that can distract us from pursuing a meaningful purpose. Stay away from lofty dreams of what might be and do not get mired down by what has happened in the past. Live and act in the moment, for only in the present can anything truly be accomplished:
Trust no Future, howe’er pleasant!
Let the dead Past bury its dead!
Act,— act in the living Present! (21-23)
Longfellow uses the seventh stanza to laud the impact great men have had on the world even after they are dead. The footprints in the sand symbolize their achievements...things that can be witnessed long after the person who made the marks has left, but things that continue to testify to that great man's presence nonetheless, and ultimately of the value these accomplishments still offer.
Lives of great men...
...departing, leave behind us
Footprints on the sands of time... (25, 27-28)
The eighth stanza speaks of those footprints again, but focuses not upon the one who made them, but those who follow them and see what has been left behind. In this section the author speaks symbolically of life being like a raging sea:
Footprints, that perhaps another,
Sailing o’er life’s solemn main,
A forlorn and shipwrecked brother,
Seeing, shall take heart again. (29-32)
The "solemn main" symbolizes the journey of life that is often similar to a dangerously turbulent ocean. The "shipwrecked brother" symbolizes humankind, anyone who may pass by and witness the accomplishment of great men—but in this case, he is "forlorn" or without hope. The metaphor is further extended to represent how someone battered and tossed by life's angry waters might be encouraged upon seeing the achievements of others who strove not to be great in their own right, but to take action and inspire others to do the same.