Question

Which statement best explains seared in the flames of withering injustice as it is used in the second paragraph

Answer 1

Slaves had been tortured and scarred by injustice.

Answer 2

This is most evidently a metaphor.  The thing to keep in mind when analyzing literature/poetry is that if you see figurative language making comparisons/drawing parallels between two differing things--instances where the meaning is not literal such as how injustice is not really a fire and has no flames--it's a safe bet you'll have on your hands a metaphor.