Embedded Player In talking about the new rug in the Oval Office on Wednesday, we mentioned several historical quotes woven into the rug, including one from Martin Luther King Jr.: "The arc of the moral universe is long, but it bends towards justice." A number of listeners pointed out that King was in fact echoing the words of 19th century abolitionist and Unitarian minister Theodore Parker. NPR's Melissa Block talks to Clayborne Carson -- a professor of history at Stanford University and director of the Martin Luther King Junior Research and Education Institute -- about Parker, and about King's use of favorite sayings.