Great. All set? Onwards and upwards, then.
The title is the first line of the spiritual "Roll of Thunder, Hear My Cry." So, it's pretty much shorthand for how the Logan family and Mr. Morrison are trying to take a stand against the injustice against blacks by whites that is rapidly building up to a crisis—like the Wallace store boycott, or Mr. Morrison's violent defense of Papa.
And just like thunder, these events are going to shake the Logans' world.