Youth
This is a poem for young people searching for meaning in their lives. It is a poem for people not yet willing to be complacent, passive, or grimly await death. It is for people who are ready to act and to achieve, to strive and fail and learn from their mistakes. Bleak dogma, conservatism, and pessimism have no place here; life is more than "an empty dream." Young people must expend physical and mental energy to accomplish things while they are on this earth, and must seek to leave a legacy to be proud of. The poem represents the youthful, enthusiastic spirit of the United States in an era of profound flux and change.
Action
While Longfellow does advocate using the mind, he wants it to be done in an active way. One should avoid being complacent or passive, or letting oneself devolve into grief or pessimism due to the fact that life is short. Instead, it is important to train the mind to be positive and the heart to be stout. There is much to accomplish before death even though it is not easy to navigate the battlefield of life. Working and thinking and striving bring meaning and allow the soul to endure beyond the sublunary life.
Religion
This is not an irreligious poem, but Longfellow's young man is expressing his discontent with the stodgy, bleak biblical platitudes that urge individuals to focus solely on the afterlife. He does not think that life is empty and that all is worthless because it eventually turns to dust; rather, he counters the psalmist that the soul is eternal and that what one does during life matters. His is an optimistic Protestantism, not the rigid Puritanism of the 17th century.
Ephemerality of Life
The young man does not shy away from this obvious fact—life is indeed short and will be over before we know it. Every beat of our heart takes us closer to the grave, and the present quickly fades into the past. However, acknowledging that life is ephemeral allows us to make of it what we want—it allows us to act, to persevere, to take joy in the pleasures of both the everyday and the heroic. Life is sweet because it is short, Longfellow suggests.
