A Psalm of Life
Genesis inversion
Flips Genesis 3:19 ('dust thou art, to dust returnest'). Longfellow argues the curse applies only to the body, not the soul—a theological move that justifies his optimism.
Ars longa, vita brevis
From Hippocrates via Seneca: 'Art is long, life is short.' Longfellow uses it to argue for urgency—your heartbeat is literally a countdown to death.
Military metaphor
**Bivouac** = temporary military camp. Life is a battlefield where you're just camping between fights. This was written in 1838, before the Civil War made such metaphors grimmer.
Matthew 8:22 reference
Jesus said 'Let the dead bury their dead' when a disciple wanted to delay following him. Longfellow borrows the urgency: don't wait, act now.
Footprints paradox
The metaphor contradicts itself—footprints in sand wash away. Longfellow seems to know this (note 'perhaps'), but needs the image anyway.