I’m rewatching 10.18, and some of the things Metatron says to Cas seem entirely relevant again after 12.23.
Metatron: ‘What is the maddest thing a man can do?’
(Cas’s grace was hidden in a copy of Don Quixote… and the maddest thing a man can do is let himself die. At which point Cas takes on his own grace…)
CASTIEL: What we did back there was unfortunate. No more of our brothers and sisters should die.
METATRON: Brothers and sisters? Listen to you. Still spitting out the company line like anyone cares. Like we’re actually a family? When what we really are – are a bunch of glowing lights filled with self-loathing or delusions of grandeur. Or both.
CASTIEL: You shut up!
METATRON: No! If I’m gonna die, I want answers. Like, who are you now? Like, you’re obviously not an angel of the Lord. And what about all of this walking the earth like Caine from “Kung Fu” crap? Cleaning up Heaven’s messes. How many more rogue angels are there out there? And, what are you gonna do once you’re done with all that? Go back to Heaven? Please. The angel formerly known as Hannah has restored order up top. Smoothest it’s run since God cut the ribbon on the pearly gates. So tell me, Castiel, truly, what is your mission now?
And then we have this bit between Dean and Cas, as “Behind Blue Eyes” plays in…
DEAN: Hey, look who decided to show. So? You’re back? 100%? How did that happen?
CASTIEL: Um, it was Hannah. She managed to get the location of the remainder of my Grace out of Metatron.
DEAN: Awesome. I told you we were due for a win. Good to have you back, pal.
In other words, he lies. He was “due for a win” and ended up metaphorically dying. All the while convincing himself it it was the right thing…