Martin Luther King Jr. wrote "Letter from Birmingham Jail" to:
B. defend the use of nonviolent resistance.
MLKJ was in jail for using nonviolent resistance as a form of protest against racial segregation. In his letter in 1963, MLKJ defends using nonviolent resistance since he states that it is people's moral responsibility to take action rather than simply wait for justice to be done at courts. He states that "injustice anywhere is a threat to justice everywhere". The letter is an iconic text for the American Civil Rights Movement.
C. address criticisms from members of the clergy.
"A Call for Unity" clergymen said that although they agreed that there were social injustices, the didn't believe that churches should have an active role or that there should be public protests. MLKJ, in the letter, describes how the church is called to be a thermostat rather than a thermometer. He bases his arguments on religious grounds, referring to Jesus as an activist.