From Andrew Marvell's “To His Coy Mistress”:
In Marvell's poem, written in the 17th century, the narrator entreats a woman he desires to set aside her modesty and sleep with him already. The line Eliot alludes to occurs at a transition in the poem. The narrator begins by telling the woman how he would praise her if he had eternity to do so. Because time is short, however, her coyness is a terrible waste and they should put their youthful bodies to use before they wither and die.
Several images used by Marvell resonate with the The Waste Land: eternity is a desert, the woman's honor is turned into dust, the narrator's lust into ashes. These morbid images contrast with the lighter images from earlier in the poem, leading some commenters to argue that “To His Coy Mistress” is intended ironically. That reading jibes better with the world of The Waste Land, where sex is mechanical, meaningless, and destructive.
Eliot alludes to the same line earlier in The Waste Land: