I have to figure that Sam deliberately buried Dean in a way that would make it easy for him to dig himself out of his grave - that handy lighter and all. Since the writers didn’t bother with an explanation, I’m going with that one.
Not that Castiel needed any help.
I’ve been wondering if they’d get around to angels. Biblical angels - angels wielding flaming swords of vengeance; angels whose faces shine as brightly as the sun; angels filled with light and heat and power too terrible and too awesome to behold. Angels who can move the “foundations of the Temple” by the sound of their voices, who purify sinners by a burning and all-consuming flame.
Seraphim means "burning ones" in Hebrew. Do the fires of heaven outburn those of hell?
Isaiah Chapter 6: And one of the seraphims flew to me, and in his hand was a live coal, which he had taken with the tongs off the altar. And he touched my mouth, and said: Behold this hath touched thy lips, and thy iniquities shall be taken away, and thy sin shall be cleansed.
The stakes got even higher for Sam and Dean. There’s a great conversation on this episode going on here: