Explain the significance of the imagery in "Sonnet 12" by Shakespeare.

A key focus of a number of Shakespeare's sonnets, and
especially this one, is the way that the inevitable passing of time is going to rob his
beloved (the person addressed in his sonnets) of his beauty. There are a number of
solutions that are suggested, but here the speaker of this sonnet says that the only
thing to do is for his beloved to have children, so that his beauty can "cheat" death
and live on in the form of his progeny.

Bearing this
overall summary in mind, let us consider some of the imagery to do with the
rapaciousness of time and how it is depicted. The poem starts with the speaker looking
at various natural sights and seeing how the passing of time effects them. The "brave
day" is now "sunk in hideous night" and the violet is "past prime." Now, the "lofty
trees" are actually "barren of leaves," and "summer's green" is all "girdled up in
sheaves." The image that the speaker presents is one where nature's beauty in the
fullness of summer has now passed and nature is "dying" with the onset of winter. This
prompts the speaker of the poem to think of his
beloved:

Then
of thy beauty do I question make, 
That thou among the wastes of time must
go,
Since sweets and beauties do themselves forsake
And die as fast
as they see others
grow;

Unfortunately, the
beloved must go "among the wastes of time" and decline and wither, just like the beauty
of nature that the speaker has just described. Because of this, therefore, the poem ends
with the only advice the speaker can give in this
situation:

And
nothing 'gainst Time's scythe can make defence
Save breed, to brave him when
he takes thee hence.

Thus the
imagery employed presents the passing of summer and the onset of winter with the
inevitable "death" of nature, which allows the speaker to meditate on the ephemeral
beauty of his beloved and what he must do as a result.