Martin Luther King Jr. (bottom right) listens to gospel singer Mahalia Jackson during the March on Washington on Aug. 28, 1963. Bob Parent/Getty ImagesEvery now and then, a voice can matter. Mahalia Jackson had one of them. Known around the world as the “Queen of Gospel,” Jackson used her powerful voice to work in the Civil Rights Movement. Starting in the 1950s, she traveled with Rev. Martin Luther King Jr. throughout the South and heard him preach in Black churches about a vision that only he