in his letter to Birmingham Jail how did Martin Luther King jr. describe the purpose of nonviolent direct action

Marthin Luther King jr. justifies the nonviolent direct action saying that Birmingham is full of injustices towards the black community and states that all the instances for negotiation or persuasion had not worked until then. The only way to make some changes, to his eyes, was through nonviolent direct action which would create enough "tension" and a state of crisis that the community's only could not ignore. Although elections brougth a less segregationist mayor, Luther King jr. claims that he was still segregationist and nothing would change. Non violent direct action would make the problem so evident and hard to ignore that eventually it will lead to the negotiation. Therefore, an instance of negotiation is the main purpose of nonviolent direct action.

Sometimes by living in a confort zone, we can't see our defects or mistakes, when something unexpected takes us out of that zone, we need to adapt and by adapting, we "grow". Juther King jr. thought that "something unexpected" was nonviolent direct action.