Patty Griffin is a storyteller. Rarely confessional or self-indulgent, she tells tales, assumes personas and takes the listener deep into the lives of her characters. Each persona has her or his own musical interpretation, deepening and strengthening the voice. In “Up to the Mountain (MLK Song),” Griffin assumes the voice of Dr. Martin Luther King, Jr. and puts herself into to the head and heart of a man working for a vision and a dream.