Analyze sonnet75 by edmund spenser?

Question

75. ONE day I wrote her name upon the strand,
but came the waves and washèd it away:
again I wrote it with a second hand,
but came the tide, and made my pains his prey.
Vain man, said she, that dost in vain assay,
a mortal thing so to immortalize,
for I my self shall like to this decay,
and eek my name be wipèd out likewise.
Not so, (quoth I) let baser things devise,
to die in dust, but you shall live by fame:
my verse your virtues rare shall eternise,
and in the heavens write your glorious name.
Where whenas death shall all the world subdue,
our love shall live, and later life renew.

Answer 1

The poem creates a thematic contrast between impermanence (the name in the sand, connected to how the bodies of the lovers will die) and immortality (their love will be eternal, both in his poems and when they meet in heaven.)