What is the main point of writing the poem "Ozymandias"?

The overarching theme of the poem "Ozymandias" is the transience of human life and its achievements. Ozymandias was a great Egyptian pharaoh, otherwise known as Ramasses II, who once built a huge statue of himself. But now, due to the passing of several centuries, the statue lies in ruins, reduced to a sad collection of fragments decaying in the desert. However, the pedestal still remains, and the inscription on that pedestal reads as follows:

My name is Ozymandias, king of kings:Look on my works, ye Mighty, and despair!

The inscription is an expression of the pharaoh's monumental arrogance. He genuinely believed that his deeds upon this earth would make him immortal. Yet his great statue lies in ruins, showing that however grand, however important we think we are, we must all one day succumb to the ravages of time.