From "Supernatural: Sympathy for the Devil (#5.1)"
I am completely and utterly through screwing around. The war has begun. We don't have our general. That's bad. Now, Michael is going to take his vessel and lead the final charge against the Adversary. You understand me?
How many humans die in the crossfire, huh? A million? Five, ten?
Probably more. If Lucifer goes unchecked, you know how many die? All of them. He'll roast the planet alive.
There's a reason you're telling me this instead of just nabbing me. You need my consent. Michael needs my say-so to ride around in my skin.