What does Martin Luther King, Jr. say about resentment in his "Letter from Birmingham City Jail"?

In his "Letter from Birmingham City Jail," Martin Luther King, Jr. uses the word resentment in a paragraph relaying to his readers the social injustices African Americans suffer in an effort to explain why African-American people cannot simply wait for society to become more just. Towards the middle of the letter, King uses a very long sentence to list social injustices, which culminates in the following clauses, one of which contains the word resentment:

When you are harried by day and haunted by night by the fact that you are a Negro, living constantly at tiptoe stance, never quite knowing what to expect next, and are plagued with inner fears and outer resentments; when you are forever fighting a degenerating sense of "nobodiness"—then you will understand why we find it difficult to wait.

In his letter, King is responding to an earlier letter written by clergymen and published in the Birmingham Post Herald. In their letter, the clergyman said that, while they opposed segregation, they also opposed protest—even nonviolent protest—against segregation, proposing instead that African Americans simply continue to wait patiently for justice to be served. King uses this paragraph to argue the absurdity of the notion of simply waiting.

The word resentment can be defined as the feeling of "indignation at some act" thought to be injurious or unjust (Random House Dictionary). Resentment is acted upon outwardly because the emotion drives us to want to combat the unjust circumstance with the hope of creating change. Since resentment is acted upon outwardly, King refers to "outer resentments," which he also juxtaposes with the "inner fears" felt by African Americans that makes them feel and act upon their "outer resentments." King uses the earlier clauses of the paragraph to describe the social injustices creating both "inner fears and outer resentments," such as lynch mobs, segregation, the "airtight cage of poverty," and humiliation. He then ends the paragraph by asserting the urgency of fighting for justice now and pointing out there is a "moral responsibility to disobey unjust laws" to fight against injustice now.