I don't know if this has already been recommended. When you think Marvin Gaye, it's the gut-wrenching, highly emotive vocal style and incredible lyrics that immediately come to mind. This song is curious, yet not unique to Marvin in that it manages to capture those same Marvin-qualities in a purely instrumental track. The vocal version of this song is great too, and I don't mean to imply that the vocal version is somehow inferior, however the vocal and instrumental versions leave me with completely different emotional impressions. The vocal version is so much more overtly full of desire and pure lust, the instrumental version by comparison feels so much more uncertain, longing, and subtle. For me, it's the subtlety and grace of this instrumental version that make it so compelling.