"Carry On/Questions" (Crosby, Stills, Nash & Young)

I'm not just a fan of CSN (and sometimes Y); I'm a fan of Stephen Stills, specifically.  He's one of the few rock musicians I know of who could tackle everything from acoustic folk to blues-drenched R&B and actually make it sound natural.
Case in point: his mini-suite "Carry On/Questions" from the album Déjà vu (1970).  It begins with this galloping acoustic portion that feels almost like an Indian raga before seamlessly transitioning into this funky Hammond organ-driven groove.  It's two things that probably shouldn't work together, but they do.
The track consists of two songs that Stills had been working on but never quite finished.  They needed an opening track for Déjà vu, and bandmate Graham Nash suggested they open with a suite in the same vein as "Suite: Judy Blue Eyes" from their debut.  So Stills took his incomplete composition "Carry On," which is basically a message to his bandmates to persevere, and melded it with "Questions," another incomplete composition that had been knocking around since his days in Buffalo Springfield. 
What makes the track hold together (apart from the note-perfect instrumental backing, which features Stills on both acoustic and lead guitars as well as organ, bass, and percussion), is that three-part vocal blend.  My favorite part is the a cappella transition, where they intone Love is coming / Love is coming to us all.  Gives me chills every time.