There wasn't anything he could say to Jacob; an apology didn't even cut it, he didn't think. Castiel kept his eyes downcast and said, "I don't think there is anything I can do. I'm sorry."
Dean's outburst was no less comforting and the angel glanced back to look at him with a knotted brow. "Dean, please do not get mad." Because they didn't know what would happen if he got angry yet. That wasn't something he wanted to test when there were two humans in the room - one that was defenseless as is.
"We need to leave. Where do you need to go with him, Jacob?"