Wait…wait I’m having a coherent thought about SPN 14.08…look, yes I know everything is on fire, but this is actually still in keeping with S14′s more hopeful tone and forward progression.
When Castiel said yes to Lucifer, it was in a frame of mind where he really thought he had no other role, nothing else to offer, no other worth, except sacrifice himself. It was right after the angel Ambriel told him “You help. But Sam and Dean Winchester are the real heroes. So, if the Darkness is still alive and she’s pissed… and she kills us… no big loss.”
What we’ve been seeing from Castiel in S14 is a growing awareness of his own sense of worth, which he vocalized earlier this season, “I had Sam and Dean. But I had something else that was extremely helpful. I had myself. Just the basic me, as, uh…as Dean would say, without all the bells and whistles.”
Castiel’s deal to save Jack seems more parallel to Dean saying yes to Michael. Dean and Cas aren’t at those points driven by a conviction their only worth is to sacrifice for others or they are failures if they don’t save others. Dean says yes to Michael to save Sam and Jack and keep the rest of his family from getting hurt because there really seems to be no other way–he does that for family. Castiel does it to save their son, because there really seems to be no other way–and not in a headspace where he thinks that’s all he has to offer anyone and I feel Dean was past that too when he said yes.
Like Michael said regarding Dean’s choice, it was because of love. Of course, Michael’s “drowning” possession and the Empty gooey blackness represent trauma and mental illness (it’s not like you snap a finger and those disappear, even if you do get better, anyway) but the character development has happened and they are in a healthier place. Not the finish line, but definitely closer.