when it comes down to it, it says a lot about Dean and Cas’ relationship that the show is emphasizing Lucifer’s “getting into character” as literally saying Dean’s name.
The first time he really put on the act, he rolled his eyes out of Dean’s vision, lowered his voice and said his signature line: “Hello, Dean.”
Then tonight he gets a phone call, says “It’s SHOWITME”, sits on his throne and puts on the act once again with another, resounding, “Hello, Dean.”
And then to Sam, he tells him how he’ll put the act on again when Dean comes back and he’ll say Dean… no wait, lowers his voice and says, “Dean…” softly instead. With more resonance and care. The way Cas says it.
To Lucifer, and to the audience, we’re forced to see what really defines Cas in those moments. What it takes to put on the act OF Castiel. And what it all comes down to, is one thing: Dean.