Laughter sprinkles through the very amiable Stephen Marley’s conversation. Though when he speaks about the value of reggae music’s one love, socially conscious and political messages, he becomes quite serious.

“It’s most important,” declares Marley, the eight-time Grammy winner and second son of the music’s legendary purveyor, the late Bob Marley, and his vocalist wife, Rita Marley. “That is the purpose of reggae music...