Answer: It reinforces the idea that even those with great fame cannot escape the slow decay of time.
In the poem, the author is talking to a man who has travelled to Egypt. The traveller says that he came upon the ruins of a statue, and the statue belonged to Ozymandias, or Ramesses II. The inscription stated the name of the ruler and asked the reader to look upon the enormous splendour of everything Ozymandias had built. However, only the ruins of the statue remained, and everything else around was sand. The poem implies that even Ozymandias can be forgotten, and a kingdom like Ancient Egypt destroyed. It implies that time does not forgive anything, and even the most incredible things end up fading and dying over time.