Why was James Reeb important?

Reeb was a Unitarian Universalist minister who was beaten to death in Selma, Alabama in 1965 for his for his support of Martin Luther King's efforts to organize a march from Selma to Montgomery. Although he was not the first person to die in the unrest at Selma (Jimmy Lee Jackson, an African American hospital worker, had been killed two weeks before), Reeb's death focused national attention on the movement and was a major impetus for the drafting and passage of the Voting Rights Act of 1965. 
Reeb's death resulted in protests and vigils by thousands around the country, and he was eulogized by Martin Luther King. In his eulogy, King described Reeb as "a witness to the truth that men of different races and classes might live, eat, and work together as brothers." The same night of King's address, President Johnson gave a televised speech alluding to events in Selma and urging Congress to pass the Voting Rights Act.
Beyond the political significance, Reeb's death helped foment moral outrage against southern segregationists.  The details of his case—first, that he was a white minister from Massachusetts; second, that he was brutally bludgeoned to death; third, that it took several hours for him to receive treatment at a hospital; and fourth, that of the four men indicted in his case, three were acquitted and one avoided prosecution by fleeing to a neighboring state—were such that the popular opinion went decisively against the segregationists. Indeed, Johnson himself aligned with the protesters in his speech for the Voting Rights Act, using a popular phrase of the movement, "We shall overcome."
http://archive.uuworld.org/2001/02/feature2.pdf

https://www.uuworld.org/articles/memoir-kings-eulogy-james-reeb