"Wait," we hear you say. "You put Luke here instead of in the character section? You've been smelling too much printer ink, Shmoop people." Yes, it's true: Luke is a character, not a symbol.
But considering that the whole film leads up to his big reveal at the end, and considering that he literally has no dialogue in the entire movie, it's going to be pretty hard to eke out a character description without diving into the earlier movies. (And if you need to do that, we've got you covered.)
Wherever they're going with him in this new trilogy, you need to look to Episode VIII to see it.
For now, Luke is what we like to call a MacGuffin: a plot device designed to move the characters through the story. The joke is that it doesn't really matter what a MacGuffin is; the only thing that matters is that the characters want it. Examples include the briefcase in Pulp Fiction, the black bird in The Maltese Falcon, the jewels in your average heist film, the secret plans in a spy caper, and basically every darn thing Indiana Jones ever went after.
(We'll leave it to Alfred Hitchcock, who seriously loved him some MacGuffins, to describe it best.)
And yes, people can be MacGuffins, too. In this case, Luke is fantastically important to the future of the galaxy. The First Order is on the march, they've killed all the Jedi but him, and if they can settle his hash, then they're sitting pretty. Luke, still reeling from losing his nephew to the dark side—and, oh yeah, watching said nephew butcher all of his other apprentices—goes into hiding to contemplate where it all went wrong and keep himself safe until…
Until what exactly?
Again, that's a question for later films, though we're guessing he figures the Force will provide. What's important is that the good guys want to find him just as much as the bad guys do, which prompts a massive hunt for BB-8 (who has the missing map piece showing where he is).
And yet, at the same time, Luke is more than just a means of moving the story forward. As we talk about in the "What's Up With the Ending" section, it's possible to pack a whole lot of character into one little scene. All Luke has to do is turn around and show us that haggard, grief-stricken face to let us know that he's felt every agonizing thing he's seen.
MacGuffin he may be, but prick this one and he most definitely bleeds.