The speaker says that he always hears "Time's winged chariot hurrying near" (line 22). In this line, time is personified as someone driving a fleet and fast-moving vehicle, signifying how quickly time seems to move. The speaker is attempting to convince his mistress, who is behaving coyly and standoffishly by refusing to sleep with him, that they should, in fact, sleep together now because life is short and time passes so swiftly. For now, they are both young, beautiful, and passionate, and he wishes that she would have no concern about her "quaint honour" and simply give up her "long-preserved virginity."
The speaker describes death, the "marble vault" into which her body will eventually be deposited, and how the worms will eventually eat away at her. Her body will, he suggests, be assailed by those worms no matter what, and so what good would her virginity be then? The speaker employs this specter of death, suggesting that it is closer now than it seems, as a way of reinforcing his claims about time. In youth, we may feel that we have lots of time, but the older we get, the faster it passes, and the speaker uses this personification of time, as driving a winged chariot, to emphasize how quickly youth and beauty will fade and passions cool as the couple ages.