The sign outside the church reads:
"He ain't heavy,
He's my brother."
-The Hollies (And Jesus)
This is a biblical reference first and foremost. Secondly, it's the name of a song, popularized by The Hollies in 1969. However, it's also probably an innuendo to Sam and Dean's relationship, since one is always having to carry the other through a difficult time.
This week's cover names of Allman and Betts refer to the Allman Brothers Band - Gregg or Duane Allman and Dickey Betts.
The church featured in this episode was used as a filming location once before, in season 2's Houses of the Holy (2007) . Both the interior and exterior match.
'Paint It Black' is a song by the rock band The Rolling Stones.
The church in the opening scene is St. Andrew's Wesley United Church in Vancouver, Canada.