Shakespeare's Sonnet 18 summary?

Shakespeare's sonnet begins with a very straightforward
question:  "Shall I compare thee to a summer's day?"  Then, there is a straightforward
answer:  "Thou art more lovely and more temperate."  And, the rest of the sonnet
supports his argument that the poet's love will remain constant while nature changes. 
For instance, in lines 7 and 8, the poet writes that nature changes its course and
"every fair from fair sometimes declines."  But, "thy eternal summer shall not fade." 
In other words, everything that nature produces--a summer's day, including--is
transitory, but the poet's love is eternalized in verse. Summarizing his argument with
the  sonnet's couplet, the poet writes that as long as men can see and read, the beauty
of his love shall be preserved in his verse.:

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So long as men can breathe or eyes can
see,

So long lives this and this gives life to
thee.

Ironically, however,
the subject of the sonnet receives immortality only because of the verse, and so, in a
sense, the argument for the immortality of the loved one is somewhat
flawed.