SPOILERS for Star Wars: The Force Awakens. Do what you must.
During the build up to Star Wars: The Force Awakens there was a lot of speculation about which new characters were and weren’t Jedi. Obviously, Daisy Ridley’s Rey is the one with the greatest aptitude with the Force, using the Jedi mind trick, snatching the lightsaber from a great distance, and such, but a member of the Star Wars universe, Samuel L. Jackson, just brought up in interesting point about John Boyega’s Finn and why maybe we shouldn’t be so quick to judge his ability in that realm.
The star of Quentin Tarantino’s The Hateful Eight, who played Jedi master Mace Windu in the prequels, recently said the kids in Star Wars: The Force Awakens could use some additional lightsaber training. Appearing on Watch What Happens Live, when the subject of Rey’s Force ability comes up, Jackson threw in a nugget about Finn, saying:
Well, apparently he’s [Finn] got some midi-chlorians of he wouldn’t have been able to turn the fucking lightsaber on.
As we learned in The Phantom Menace, midi-chlorians are the microscopic lifeforms that live within cells and let the Force speak to us if their numbers are high enough. Finn obviously has some midi-chlorians in his blood because they exist in the cells of all living beings.
Contrary to Jackson’s statement, it’s been a pretty well established fact people with no particular ability with the Force can still use lightsabers. In the original concept for Star Wars, they were not the exclusive weapon of the Jedi and the Sith, and there’s early Ralph McQuarrie art of stormtroopers using them. In The Clone Wars, which is still considered canon, there are couple of instances of non-Jedi or Sith using them, notably General Grievous (who also handles them in Episode III) and Pre Vizsla, among other instances around the galaxy far, far away.
The reason they’re not used more widely is because, unless you’re Force sensitive, they’re not the most convenient choice. They’re kind of unwieldy, and if you’re using it to block shots from a blaster you generally need the Force to help predict that. Powered by Kyber Crystals, the weapons form a kind of symbiotic relationship with their Jedi—Jedi use the Force to select the crystals. Though they form this bond, that doesn’t mean non-Jedi can’t use lightsabers, it’s just that, for a variety of reasons, a blaster or some other weapon is usually a better choice for the non-Force inclined.
All of this isn’t to say that Finn may not turn out to have some aptitude with the Force, we just don’t know at this point. It would be awesome if he has some Jedi in him, but the simple fact that he was able to use a lightsaber doesn’t automatically mean the Force is with him.