According to the speaker, all things on earth decay: they are transitory or temporary:

Nor gates of steel so strong but time decays?

Not even steel can stand up against time.

The speaker asks how, therefore, something as fleeting as beauty can withstand the power of time? He personifies time or "Time" as a person whose swift foot ruins beauty. In a world in which all things quickly age and decay, what can preserve the beloved? The narrator says his ink--the words he writes--can preserve the record of his love for the beloved long past the time when he and his love have physically decayed.

The power of verse to preserve a loved one's memory against the ravages of time is a recurrent theme in Shakespeare's sonnets. Words offer a form of immortality the physical world cannot.

Sonnet 65 by Shakespeare presents the nature of things on earth as temporary and slaves to the destructive nature of time. The narrator states that mortality holds power over all things, even those that seem permanent, like the sea or stones. He suggests that beauty has the fleeting nature of a flower and then uses breath as a metaphor for summer. Perhaps the most obvious example of the temporary nature of all things is in line 7:

When rocks impregnable are not so stout

First, the narrator describes rocks as impregnable, which means strong and immovable, but then he explains that these rocks are actually not as strong as they seem when in contact with the power of time. He personifies time by explaining it as having a swift kick that nobody can stop. At the end, though, he explains that there may be one miraculous exception:

That in black ink my love may still shine bright.

He claims that his writing may stand against the fleeting nature of all other present things.