The poem plays on a double meaning. At first the speaker sounds relaxed, even cheerful: always ready for a vacation, practicing how to be simple. The title, "Practice makes perfect," suggests a kind of daily training in letting go of fuss and ambition. But the last stanza shifts the ground. The same body that is "prepared for his journey" is headed "down in the grave," so the vacation starts to look like a rehearsal for death.
The middle lines hold the poem's hinge. The speaker asks us to imagine "the prizes we desire in the present," which hints that the things we chase now, and the rewards we hope for, may count for little when set beside that final trip. Wanting is tied to the present moment, and the present is all we have.
The mood is calm, a little wry, and quietly sobering. The speaker doesn't seem panicked. There is acceptance here, as though being simple and being ready to die are the same skill.