Martin Luther King uses the image of a festering boil in order to convince the church of the need to bring the injustice of racism to light. Perhaps the most important aspect of the metaphor, along with the ugliness and toxicity of both a boil and racism, is the fact that to open a boil is a painful and scary process. Just as it is easier in the short term to let a boil stay untouched, due to its sensitivity, the church did not want to address the issue of racial injustice due to the uproar and it would cause in its communities.
Dr. King uses figurative language to compare the pus-flowing ugliness of a popped boil to the violence and disorder that must arise from facing the problem of race relations head on. In doing so, he both addresses the toxicity and ugliness of racism in society, and also the need to go through the painful experience of bringing it to light.
