What is the effect of the rhyme and repetition in the first six lines of Sonnet 29 by Edna St Vincent Millay?

I teach my students that the meaning of a poem is one
derived (that comes from) from personal interpretation and support.  So, what I offer
you is my reasoning behind your question.

To truly
understand the effect of rhyme and repetiton in a poem, one must look at the poem in its
entirety.  The poem is about a woman's love and how it has been lost because love is as
changing as nature and the heart is too slow to learn something that changes so
swiftly.

As for the rhyme of the poem, you cannot look at
only the first six lines based upon the fact that the scheme is as follows:
a,b,a,b,c,d,c,d,e,f,e,f,g,g (which shows the poem is written using the Shakespearean
sonnet form with the last two lines as a rhyming
couplet).

The rhyme of the poem has the effect of the
typical Shakesperean sonnet:

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The Shakespearean sonnet affords two additional
rhyme endings (a-g, 7 in all) so that each rhyme is heard only once. This not only
enlarges the range of rhyme sounds and words the poet can use, it allows the poet to
combine the sonnet lines in rhetorically more complex ways. Shakespeare often gave
special emphasis to the break between the second and third quatrains (equivalent to the
major break between the 8 quatrain lines and the 6 tercet lines in the Italian sonnet),
but he also paired and contrasted the quatrains in many other ways, creating a great
range of argumentative or dramatic effects.

Shakespeare
invested the couplet with special significance. It often summarizes or characterizes the
musings of the three quatrains in a sardonic, detached or aphoristic voice, standing in
some way aloof from the more turbulent and heartfelt outpouring of the
quatrains.

As for the effect
of repetition in the poem, "pity me" repeated three times in the first six lines, it
shows the narrator's need for empathy from the reader.  What this does is asks the
reader to connect to the narrator.  The narrator wants the reader to feel pity for her
based upon the fact that she is unable to know true love.  Her love's desire for her is
gone.  She has the final realization that love is only known by
nature:

love
is no more

than the wide blossom which the wind
assails,

than the great tide that treads the shifting
shore,

strewing fresh wreckage gathered in the
gales,

So, in the end, the
effect that the rhyme and repetition have on the poem is one that exists so as to pull
the reader in so that they may empathize with the narrator and to fulfill the scheme of
a Shakespearean sonnet.