What is the extended metaphor from "The Chambered Nautilus":  "low vaulted past" line 31, "each new temple" line 32, and "unresting sea" line 35?

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mwestwood eNotes educator| Certified Educator

The extended metaphor in "The Chambered Nautilus" by Oliver Wendell Holmes is a comparison between the growth of the nautilus that must "leave thy low-vaulted past" for a larger chamber to the growth and spiritual development of the human soul.

The theme here for Holmes is that it is important for people, as children of Nature, to continue to build a nobler, loftier, more spiritual existence during their lives;  this growth should continue until death.  Holmes's use of the "unresting sea" connotes this continuation of improvement in the soul.