Jiren says that his wish is bring his master Kitchen back, he knows it's something selfish but he's okay with it, that's what he wants, Toppo says Kitchen was the person Jiren most cared about... but he died, Jiren failed trying to protect him and in fact he died before recognize Jiren as his successor. That's why Jiren trains so hard and is so devoted to justice, that's what he learned from his master when he was a kid and he fights so no one else needs to die for his weakness again.
Then Vegeta shits on him because if that happened long ago he should have accepted his master's death long ago, Jiren gets angry for that and attack, Vegeta says that Jiren is having a mental breakdown (so apparently Jiren's emotional damage was in the outline, kek), this is their chance to fight and win (and yes, Vegeta is the one that tells Goku to fight together, Piccolo even mentions how impressive is that Vegeta swallowed his pride and did such a thing).
At the end Vermoud says that Jiren is strong enough to fight them, but he will have a hard time with they because he can't deal with people that fight together, that's why he always worked alone even after join the Pride Troopers. Also Vegeta and Goku mention their training with Whis and Beerus asks if he ever tried to give Goku and Vegeta lessons for team work and Whis laughs because at this point he even forgot he did. Next chapter is Goku and Vegeta finally fighting together (like Whis wanted) to beat Jiren (a callback to how Whis mentioned in RoF that if Goku and Vegeta fought together, even someone like Beerus would have a hard time)
Manga Jiren is best boy, he's pure and wants his master back, he has been training and saving the universe in order to never lose someone he loves again, following the teachings of Kitchen and trying to be the perfect warrior his master wanted him to be, he will win, wish him back and protect everyone as the perfect warrior because that's what Kitchen wanted.