In Edgar Allan Poe's poem "A Dream Within a Dream," the lines you mentioned reflect the central theme of the poem, which grapples with the nature of reality and the ephemeral quality of life. Specifically, the following lines emphasize the fleeting and insubstantial nature of existence:
"I hold within my hand / Grains of golden sand -- / How few! Yet how they creep / Through my fingers to the deep, / While I weep! While I weep!"
These lines illustrate the struggle of holding onto something precious (the grains of sand) while experiencing the inevitable loss of it slipping away, highlighting feelings of despair and helplessness. The imagery of sand slipping through fingers serves as a powerful metaphor for time and the transitory nature of life, encapsulating the poem's exploration of dreams and reality.
If you're looking for a deeper analysis or specific examination of the poem's themes, feel free to ask!