He wants to protest- he's developed a new appreciation for his father after actually meeting him, speaking with him, a new Wisdom and a slight understanding of His plan. Dad gave him a pat on the back, and now he's Number One Dad again.

Dean's steamrolling him, though, and Cas curls in on himself as he listens. An unconscious thing that makes him look smaller, especially without the trench coat and suit padding. Involuntary human reactions were... dicks. The wince that accompanies his speech is completely accidental as well, and he can't quite wipe the look away, hard as he tries. "I was wrong. Humanity is... so much more. I have only been one for months, and it is... a greater challenge than anything I experienced as an angel. My chest... aches. Constantly. I feel things that... I can't even explain, except that they hurt, and I...

His eyes flick back up to Dean's, wide and sincere and as easy to read as a book. "I will do anything to fix this. Anything you ask of me. Anything you require, name it."