Let me start off by saying that I went into the show thinking that Kripke, Sera and the rest of the creators had been violating the rules of their own universe.  By the end of the episode, I’ve been convinced that not only have they stuck to their own rules, but they managed to throw a few curves this season thanks to some brilliant misdirection.  Well played, Kripke.

As has been par for the four seasons of Supernatural, this season finale begins with a montage set to Kansas’s Carry on My Wayward Son.  This has been a Supernatural tradition that the fans look forward to almost more than anything else on the show.  I think if Kripke ever did away with this, the fans might be out for blood.

And speaking of blood, immediately following the flashbacks we get another flashback.  This one to a convent circa 1972 somewhere in Maryland, where a demon possesses a priest.  The next morning, we’re treated to a kind of a fun little sermon where the demon calls the convent a nun factory and mentions the fact that his dad is sealed under the ground that the convent is built on.  Then the priest’s eyes flash yellow. 

It’s Azazel – which kind of explains why the sermon of evil was so entertaining. 

Azazel slaughters the eight nuns and manages to get his daddy on the line.
  Turns out that Azazel is the son of Lucifer, and in order to get free, Lucifer needs Lillith to break the 66 seals.  But first, to get Lilith free, Azazel needs to find a special child. 

Pay attention to that wording.  It’s going to be important later.

In some abandoned house somewhere Sam angsts over his fight with Dean to Ruby.  Ruby tries to console him with the idea that the brothers can reconcile after Sam ends Lilith and the threat she posed.  But Sam doesn’t think he’ll survive the end. 

Back at Bobby’s house, Dean is going through similar manly pain.  Bobby suggests that Dean give Sam a call, but Dean refuses.  After all, didn’t he say the exact things to Sam that his dad did?  Which prompts Bobby to unleash his awesome powers of smackdown.  He tells Dean that he’s a better man John, and that he can make things right with Sam when John wouldn’t.

Sam and Ruby track down one of Lilith’s minions – a baby sealing demon that Ruby says is ‘Lilith’s personal chef.’ 

Ew. 

They take her back to their abandoned shack and torture Lilith’s location out of her.  Ruby tells Sam that they need to keep the demon alive so that Sam can feed on her blood.  Which prompts the demon to let the human host back into the driver’s seat and force Sam to confront what he’s about to do: take the life of an innocent human.