So Cas took Metatron’s grace, and now they’re off on a trip to go get Cas’ grace back. Reminding us that Cas’ stolen grace will deteriorate again, and probably soon. And that means that Cas will be driving around with the direct temptation of just using Metatron’s grace for himself as Metatron drags his heels like he’s bound to do.
Which means that Dean and Cas’ stories will be paralleled, because they will both be faced with caving in to what they want- for Dean it’s violence, and for Cas it’s not dying- and they’ll have to make the hard choice. And as a reminder, Cas lost his grace and faced his mortality at the same time that Dean faced Sam’s mortality, Cas stole the original grace within two episodes of Dean taking on the Mark, and that grace faded at the same rate as the Mark affected Dean psychologically.
What’s great about this parallel is that in both cases, choosing each other is a viable solution: Cas as the Colette to Dean’s Cain, and Dean as the reason that Cas has to either become human again, or at least get his own grace back and end the cycle of shittiness. That’s a good parallel uwu