Longfellow's poem "A Psalm of Life" is a celebration of life, as the title indicates. The narrator says we should focus not on death but on the here and now. This life, he states, is vital and important. What we accomplish in our lives matters.
The word "footprints" appears twice in this poem. Longfellow tells us to "act in the living present!" He encourages us to try to leave behind something that will last. To do so, he uses the image of "footprints" left behind by great men. These are the acts these men performed as well as the works they produced. Because these men aspired to greatness, their accomplishments can act as inspirations, as "footprints" we can follow. These footprints tell us that we, too, can live "sublime" or extraordinary lives. When we do so, we also will leave behind "footsteps" that others can follow as they pursue the path of the exceptional. In other words, we can follow the path of great men who have come before us and then leave a path that provides inspiration for other, future people.