Henry Wadsworth Longfellow is an American poet who wrote during the Romantic period. Romanticism in literature is a direct reaction against the Age of Reason or Rationalism. Some key features of Romantic literature are: a reverence for nature, an emphasis on the emotions instead of logic, a focus on the individual, a general belief in the goodness of humanity, and an emphasis on a carpe diem attitude.
"A Psalm of Life" invokes mankind to act in the present and adopt optimism because Longfellow is a romantic poet. The optimism and "seize the day" attitude are encompassed by several lines within the poem. "Life is real! Life is earnest!/And the grave is not its goal;" shows an excitement toward life and a get up and do something attitude. Longfellow says that "time is fleeting" so "be not like dumb, driven cattle." Again, time is short, go out and do something unique. Be yourself and do it now, because "let the dead past bury its dead." In other words, stop focusing on all of the negative parts of the past. Look to the future and its hope.
Longfellow's encouragement to be optimistic is encompassed when he writes "we can make our lives sublime." Not just happy or pleasurable, but sublime. This is a very romantic line because it focuses on the individual, the emotions, and belief that it is all within man's power and capability.