As Gladys Knight's recording of "Neither One of Us (Wants to Be the First to Say Goodbye)" climbed the charts in 1973, she asked Jim Weatherly, the song's composer, for another love song. He sent along "Midnight Train to Georgia," which Cissy Houston had recorded a year earlier.

Envisioning a seductive, punchy instrumentation behind her, Ms. Knight turned to producer Tony Camillo for an Al Green feel. Within weeks of its release 40 years ago in August, Ms. Knight and the Pips' "Midnight Train to Georgia"...