What is the message of Percy Bysshe Shelley's poem "Ozymandias"?

The meaning or themes of Percy Bysshe Shelley’s poem
“Ozymandias” are fairly straightforward and are also highly traditional. Basically, the
poem reminds powerful people that their power is only temporary. However much powerful
people may wish to think that their power is immortal, they are only deceiving
themselves. Earthly power is mutable, and indeed all human beings (Shelley may imply)
need to remember this lesson.

What makes all these meanings
highly memorable, of course, are the techniques Shelley uses, including the
following:

• The speaker of the poem doesn’t
  himself preach; instead, he merely quotes the words of another person (the "traveller"),
  so that we are more likely to listen and consider the opinions the poem expresses. The
  speaker himself does not come across as a mere propagandist; rather, he presents himself
  as an honest reporter.


• Although the poem has obvious
  relevance to (and implications for) powerful people of the present day, Shelley keeps it
  from seeming a mere piece of contemporary political propaganda by making it a lesson
  about powerful figures of the past.  Readers are more likely to listen to a general
  moral lesson than to a lesson that seems aimed at particular political targets of the
  present.


• By keeping the poem short, Shelley gives it
  added impact and increases the likelihood that it will be read.  Few people have taken
  the time to read Shelley’s long political poems, but many, many readers have read and
  been moved by “Ozymandias.”


• By presenting this message
  about mutability in the form of a sonnet, Shelley deals ironically with a genre often
  associated with love.  However, Shakespeare’s sonnet 55 is similar in various ways to
  Shelley’s poem, as are various political sonnets by Milton and Wordsworth.
  


• Shelley uses extremely vivid and memorably imagery. 
  Rather than treating his topic in vague, abstract, or general terms, he creates highly
  specific images, as when the traveller describes a statue he has
  seen:

readability="15">

. . . “Two vast and trunkless legs of
stone
Stand in the desert... Near them, on the sand,
Half sunk, a
shattered visage lies, whose frown,
And wrinkled lip, and sneer of cold
command,
Tell that its sculptor well those passions read
Which yet
survive, stamped on these lifeless things . . .
(2-7)

• Shelley uses
  irony when he lets Ozymandias speak for himself by reporting the inscription carved on
  the dead king’s crumbled statue:

readability="8">

‘My name is Ozymandias, king of
kings:
Look on my works, ye Mighty, and despair!’
(10-11)

• Immediately
  after reporting these proud and now almost ridiculous words, the traveller merely
  observes: “Nothing besides remains” (12). Rather than spelling out the lesson for us,
  the traveller, the speaker, and Shelley all let us draw the obvious conclusions for
  ourselves. The poem thus shows respect for its readers'
  intelligence.