What is the theme of the poem "Once by the Ocean" by Robert Frost?

The theme of "Once by the Ocean" is the inevitable passing
of time and its slow destruction. There is a heavily foreboding tone established at the
outset of the piece. The water and waves "shatter" into the shore and "The clouds were
low and hairy in the skies,/ Like locks blown forward in the gleam of eyes." I picture a
very gray and stormy sky.

The waves are plotting against
the shore as well. This personification of the ocean furthers the sense of
foreboding.

Great waves looked over others coming
in,
And thought of doing something to the shore
That water never did
to land before.

The reason this is
foreboding is that the speaker has the "feeling" that "The shore was lucky in being
backed by cliff."

The cliffs bring us even more evidence
towards the destruction of the passing of time. The cliffs will only last so long
against the constant battering of the waves. Erosion will eventually take over and bring
the cliffs down into the water.

Finally, a sense of
destruction at the hand of God is offered in the last
lines:

It looked as if a night of dark
intent
Was coming, and not only a night, an age.
Someone had better
be prepared for rage.
There would be more than ocean-water
broken
Before God's last Put out the light was
spoken.

God's plan dictates that everything in
nature must grow old and die. Frost gives this poem its final message by including God
as the initiator of the destruction.