Supernatural, Season 4

Dean:
Well, I feel stupid doing this, but... I am fresh out of options. So please. I need some help. I'm praying, okay? Now come on! Please.

Castiel:
Prayer is a sign of faith. This is a good thing, Dean.

Dean:
So does that mean you'll help me?

Castiel:
I'm not sure what I can do.

Dean:
Drag Sam out of here now, before Lillith shows up!

Castiel:
It's a prophecy. I can't interfere.

Dean:
You have tested me, and thrown me every which way. And I have never asked for anything. Not a damn thing. But now I'm asking. I need your help. Please.

Castiel:
What you're asking, it's not within my power to do.

Dean:
Why, cause it's divine prophecy?

Castiel:
Yes.

Dean:
So what, we're just supposed to sit around and-and wait for it to happen?

Castiel:
I'm sorry.

Dean:
Screw you. You and your mission. Your God. If you don't help me now, then when the time comes and you need me? Don't bother knocking.

Castiel:
Dean. Dean!

Dean:
What?

Castiel:
You must understand why I can't intercede. Prophets are very special, they're protected.

Dean:
I get that.

Castiel:
If anything threatens a prophet, anything at all - an archangel will appear to destroy that threat. Archangels are fierce. They're absolute. They're Heaven's most terrifying weapon.

Dean:
And these archangels, they're tied to prophets?

Castiel:
Yes.

Dean:
So if a prophet was in the same room as a demon...

Castiel:
Then the most fearsome wrath of Heaven would rain down on that demon. Just so you understand... why I can't help.

Dean:
Thanks, Cas.

Castiel:
Good luck.