What is the image Khadijah auntie recites to Layla, and what effect does it have?

Khadijah auntie recites one of Layla’s father’s poems, which ends with the line, “listen to the beating heart of the earth, and flashed of thunderous light in the heavens” (351). She says that Layla's father is speaking to them, and she says that Layla is the heartbeat for them all. Layla remembers her father getting her to feel the poem pulsing in her blood. She says that no one voice is the thunder alone, but the sound comes when all the voices speak together to demand justice.