The argument of "To His Coy Mistress," a carpe diem, can be divided into three parts. What are these three divisions?

If you wanted to summarize the poem in terms of three
arguments, simply put they might be as
follows:

1. If we had eternity, there would be
   nothing wrong with your being coy and not wanting to make love with
   me.


2. But we don't have eternity, and one cannot make love
   in the tomb.


3. If we make love now as I want, it will be
   earth shattering--we will give the sun a run for its money, as they
   say.

The three "arguments" are organized into
stanzas, so they're easy to investigate. 

Of course, the
whole is much greater than the sum of its parts.  Reducing this hyperbolic, intelligent,
"metaphysical" poem to an essay-like argument does not do it justice.