I always enjoyed playing this song on flute. It's a beautiful tune as an instrumental.

Wikipedia: Marvin Gaye (born Marvin Pentz Gay, Jr., April 2, 1939 – April 1, 1984) was a popular soul, R&B singer, arranger, multi-instrumentalist, songwriter, and record producer. He gained international fame during the 1960s and 1970s as an artist on the Motown label. His best records are still highly regarded, and he is often cited as one of the finest singers of his era.
Here's more from Soul Walking.

"What's Going On" the record.