"Mercy, Mercy, Mercy" (Cannonball Adderley Quintet)

"Mercy, Mercy, Mercy" is the title track from the Cannonball Adderley Quintet's 1966 album Mercy, Mercy, Mercy - Live at 'The Club' (which really wasn't a "club" at all, but Capitol's LA recording studios with the addition of an open bar and a bunch of partiers). 
The song is just a great little groove. 
As Julian "Cannonball" Adderley announces at the beginning of the track, the song was written by Austrian pianist Joe Zawinul, who'd gain further acclaim playing with Miles Davis on Bitches Brew (1970) and with the jazz-fusion band Weather Report throughout the 1970s.  With the exception of two verses where Adderley (on alto sax) and his brother Nat (on cornet) blow a couple of bars, it's really a showcase for Zawinul on Wurlitzer electric piano.
If you've ever played a vintage Wurlitzer--I did once at a junk shop years ago, you know it's somewhat limited in what it can do.  You basically can adjust the volume and the sustain, unless one or the other is busted.  And speaking of busted, the flat metal reeds inside the Wurlitzer, which create its signature sound, apparently break if you look at them cross-eyed.  Plus, they are/were a pain to replace and tune.  (The junk shop owner effectively talked me out of buying the thing, if you can't tell.)
Anyway, I only bring this up because of how Zawinul works the heck outta the Wurlitzer on this recording.  He doesn't fly across the keyboard or do anything too crazy; he just finds every bit of soul that's in that funky little electric piano and channels it right into every bluesy chord he plays.  He not only is able to finesse the instrument to get a mellow, almost vibraphone-like tone on the first two verses, but he gets the funk to a real boil and takes it to church on the hook and final verse.
In all, it's a song that makes you feel good when you're feeling bad, and makes you feel so bad (in a good way) when you're feeling alright.