Castiel in “Unfinished Business”

Castiel

Maybe you could fight the mark for years. Maybe centuries, like Cain did. But you cannot fight it forever. And when you finally turn, and you will turn, Sam, and everyone you know, everyone you love, they could be long dead. Everyone except me. I’m the one who will have to watch you murder the world. So if there’s even a small chance that we can save you, I won’t let you walk out of this room.