Dean and Castiel in “Unfinished Business”

Dean

What the hell do you mean you can’t?

Castiel

I mean there’s nothing left to rebuild.

Dean

Why not?

Castiel

Because it crumbled. The pieces got crushed to dust by whatever’s happening inside his head right now.

Dean

So you’re saying there’s nothing? That he’s gonna be like this until his candle blows out?

Castiel

I'm sorry. This isn't a problem I can make disappear. And you know that. But I may be able to shift it. Shift? Yeah, it would get Sam back on his feet. (Exhales sharply) It’s better this way. I’ll be fine.

Dean

Wait, Cass, what are you doing?

Castiel

Now, Sam… This may hurt. And if I can’t tell you again... I'm sorry I ever did this to you.