When hip-hop came into its own about a decade ago, soul music lost a bit of its soul. Hip-hop took with it a chunk of the fight-the-power spirit that had once belonged primarily to soul and rhythm and blues. Back in the day--as the phrase goes--Marvin Gaye, Curtis Mayfield and Stevie Wonder sang of urban blight and soul power, about disintegrating families and spiritual transcendence, about "what's going on" and living in a "pasttime paradise."
When rap came around, however, younger performers found its passionate, insistent rhythms a more fitting vehicle for the messages they wanted to deliver and for presenting...