YOU DON’T UNDERSTAND
I’ve kind of always considered this as the moment when Dean first realizes what Cas is really willing to do for them. He knows Cas is willing to die, but in the life of a Winchester that’s an easy sacrifice. Now he has this picture that tells him Cas is also willing to stick around, and keep sticking around.
And for a character who had a three season long abandonment arc (his brother, his father, people just gett’n up and leaving him all the time) that’s gotta be a big deal.
I wonder if this explains why Dean’s never lost faith that Cas will always come back to him? If this explains why Naomi couldn’t influence him, couldn’t turn him against Cas? Because Dean knows that Cas will always be there, he doesn’t have to worry about Cas leaving because he will follow Dean to his death. Literally.