While much of the focus of Star Wars: The Last Jedi has been on what will happen between Rey and Luke Skywalker, we know that there will be an entirely separate plot that sends Finn back into the First Order undercover. For a guy who had only just broken free from the organization, it would seem like going back in would be the last thing Finn would want to do, but director Rian Johnson says that's exactly why he decided to have Finn do it. He wanted to give Finn the toughest task to overcome that he could think of. According to Johnson...
Man, I would [freak out] if I were him. Just think of the moral courage it took, and how much just physically it took, to get away from the First Order. It's that thing of coming back to 'What's the thing that would be toughest to throw at each of these people?' And to go back into the machine, to put that uniform on again, made a lot of sense to me.
When we first meet Finn in Star Wars: The Force Awakens he has a breakdown following the First Order's brief firefight on Jakku. Later, when he realizes Rey plans to fight rather than run away, he looks for his own passage off the planet that will get him as far away from the First Order as possible. While Finn clearly overcame his fear to some degree in order to become part of the team trying to rescue Rey, it's unlikely he's put it all behind him, and walking right into the lion's mouth is likely not on the list of things he's interested in doing.
It seems that Star Wars: The Last Jedi director Rian Johnson was very interested in keeping all of the characters on their toes for the new film, as he tells USA Today that part of his goal in writing the story was to give each of them something challenging to deal with, where they wouldn't be able to rely on the people who helped them last time around.
And now we get to kind of put them through a meat grinder. (Laughs) And for me, part of that meant that we had to make things as hard on each of them as possible: At least part of the movie, they don't have their friends around. They've got to figure things out for themselves.
We should probably expect things won't be easy for our heroes in Star Wars: The Last Jedi. It is the middle entry in the trilogy of course. That means a lot probably won't be going their way. While it might be tough to see our favorite characters be put through hell, it will also show us just how great they are when they come out the other side.