Dumah: If we had him, he wouldn't be imprisoned. He would be put to work.
Castiel: What do you mean?
Dumah: Castiel, the angels... Our numbers were greatly diminished after the fall. No one's made new angels since the dawn of creation. We're going extinct. You would need a powerful force to make more of us.
Castiel: Jack, I've killed people who didn't deserve it... my friends... I've killed people I loved. I wish I could tell you that it... that it gets easier, that with time, it hurts less, but that would be a lie because it... it never gets easier. And those moments, they never stop hurting. But that doesn't mean that you should stop fighting. Doesn't mean that just because you made a mistake... and that's what this is, Jack. It's a mistake. That doesn't mean that you can't... can't be better, do better. I believe that. I have to believe that.