This phrase, one of the most famous in the poem, occurs in the second stanza of the first part of the poem, "The Burial of the Dead." It comes at the end of a series of images of a wasteland: "a heap of broken images" that include dry stones, dead trees, and a lack of shelter. The speaker ends this series of images by addressing an unknown person and promising to show more than "shadows." The speaker states:
I will show you fear in a handful of dust.
Dust and handfuls of dust traditionally point back to the Christian liturgy. The image of dust expresses the idea that humans are fashioned, like Adam, out of the dirt of the earth and return to it after death. In a traditional Christian burial, mourners or the priest often throw handfuls of dirt or dust on the coffin as a first step in the burial process while reciting "ashes to ashes, dust to dust" to reflect the cycle of birth and death.
In introducing this phrase, the speaker is stating an intention of emerging to speak directly about death. We fear death—the return to dust—but the speaker will help us to face that fear, which is the first step to rebirth.
In a poem about the fragmentation and seeming death of civilization and hope after World War I, this phrase helps guide us to what the poem will cover, which is death and the possibility of rebirth.
Like many of the phrases in the poem, this one has multiple sources. Two often pointed out are Joseph Conrad's The Heart of Darkness, which questions the values of Western culture, and Charlotte Mew's poem "Madeleine in Church," which searches for the meaning in mortality.