outofcharacter. There's a post that has been going around that hints to Jean's gesture of kissing his sword in ep. 17 being the same hand that he held Marco's "bone" in-- Which it is but I would also like to point out my thoughts on it. (Which they may be silly, but whatever.)
The gesture could be a representation of how his gear is the only thing that he can truly depend on during this time as it is, despite his own mentality and skills, the only thing that will aid Jean in staying alive. Which it is now his pride/honor/whatever you may call it simply because of the vow he made when he watched Marco's body burn with the other fallen soldiers.
It could've also been a prayer(/good luck charm) for the same reason; Because his gear is the one thing he can actually trust right now and because how much he's invested into his current way of life and the vow he did make, Jean wants to get out of this alive and victorious. He doesn't want his actions or all the sacrifices they had made for humanity to be in vain.
