What message is sent by the nautilus in stanza 4?

In Oliver Wendell Holmes' poem "The Chambered Nautilus," the
poet describes through the first three stanzas, the practice of sea creatures living in a shell
for a time. And when a creature decides it is time, it leaves one shell to move on to another. It
attaches itself to its new abode which becomes home, while the old "dwelling place" is
forgotten.

In stanza four, the poet seems to be speaking to one of
the shells that has been washed ashore and retrieved by him:

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Child of the wandering
sea,

Cast from her lap,
forlorn!

The poet personifies the
shell, describing it as forlorn, and continues the personification when describing that its lips
create sound:

From thy
dead lips a clearer note is born

Than even Triton blew from wreathed
horn.

The poet writes that while it
may no longer be a home, it rings in his ear (as when one places a shell to his ear to listen to
the ocean), and when deep in thought, he hears a voice singing, like the sound of the
ocean.