“I only know one truth: It’s time for the Jedi to end.” 
The recently-released Star Wars VIII: The Last Jedi trailer ended with Luke saying the quote shown above. With the movie yet to be released, we don’t know for sure what he means: Perhaps it’s a stance he takes at the start of the film, then comes to reverse it later. Perhaps it’s something permanent that shapes the future of the Star Wars universe, as the very title of the film could indicate. Time will tell. My intent in this post, however, is to look into the Star Wars universe and see what can be gleaned from things that are already in place to get a view of may come.
My guess is that Luke Skywalker and his nephew Ben/Kylo Ren discovered something about the Jedi Order that has shaken their faith in the order as it was passed on to them. The conclusions that they came to caused Ben to turn to the dark side and to seek to eliminate all Jedi and Luke to seek out the first Jedi temple and stay there to ponder on what it means to be a Jedi. We have seen precious little of Luke in canonical literature covering the period after the Return of the Jedi. For the most part, the few glimpses we see are that Luke went out seeking Jedi lore and artifacts for years after the Battle of Endor. The novel Bloodlines indicates that Luke and Ben were traveling together somewhere far away doing research approximately six years before The Force Awakens. In The Force Awakens, Leia also states that she lost Ben when she sent him away to train with Luke. Perhaps it was during this journey that Ben turned to the dark side, inspired to do so by something he and his uncle discovered together.
Ben’s fall is also deeply connected to his relationship with Darth Vader. In The Force Awakens, Han states that “There was nothing we could’ve done. There was too much Vader in him.”  Leia feels that it was Snoke that seduced Ben to the dark side and states that she sent him to train with Luke to keep him on the light side. This indicates that Ben was struggling with the dark side even before he and Luke went out on archaeological expeditions together. In addition, the knowledge that Darth Vader was Ben’s grandfather was withheld from him until it was announced to the universe by one of Leia’s political enemies during the events of Bloodlines (again, six years before The Force Awakens). Ben was about nineteen years old at the time. The shock of learning this may have catalyzed his final descent into darkness. When we see him in The Force Awakens, he idolizes Vader, speaking to his mask and stating: “Forgive me. I feel it again. The pull to the light. . . . Show me again, the power of the darkness, and I will let nothing stand in our way. Show me, Grandfather, and I will finish what you started.” 
What did Darth Vader start that Kylo Ren wishes to finish? In the SNL Skit “Undercover Boss: Starkiller Base,” when Kylo Ren in disguise asks some employees if they believe that Kylo Ren will finish what Darth Vader started, one of the storm troopers asks, “What exactly has he started?” An officer responds that he has respect for Kylo Ren and indicates that the goal is to “rule everything.”  This could very well be the case. The Visual Dictionary for The Force Awakens states that Kylo Ren “seeks it as his birthright to rule the weaker beings in the galaxy. . . [and] Kylo Ren aspires to build immunity to the light side—to succeed where Darth Vader and his sentimentality once failed.”  It may be that Kylo Ren sought to fulfil Darth Vader’s goal to rule the galaxy.
Some of Anakin Skywalker’s statements lend themselves well to his main project being galactic domination. In Attack of the Clones he tells Padmé that he believes that “we need a system where the politicians sit down and discuss the problems, agree what’s in the best interests of all the people, and then do it” and that if they don’t agree, “then they should be made to.”  He indicates at the time that he doesn’t feel like he should be the one to do it, but by the end of The Revenge of the Sith, he tells Padmé that: “I am more powerful than the Chancellor. I can overthrow him, and together you and I can rule the galaxy. Make things the way we want them to be.”  He also echoes this same offer to Luke in The Empire Strikes Back when he said: “Join me, and together we can rule the galaxy as father and son.”  His goal, as stated to Obi-Wan, is to bring “peace, justice, freedom, and security to my new Empire.”  Anakin’s political idealism led him to look towards ruling the galaxy as Darth Vader to make things the way he wanted them to be.
There was another project that Darth Vader believed very strongly in, however—purging the galaxy of Jedi. Most famously, during his duel with Obi-Wan on Mustafar, Vader proclaims that: “I see through the lies of the Jedi. I do not fear that dark side as you do. . . . From my point of view, the Jedi are evil!” Before this declaration, Palpatine taught Vader that “every single Jedi . . . is now an enemy of the Republic. . . . The Jedi are relentless; if they are not all destroyed, it will be civil war without end. . . . Do what must be done, Lord Vader. Do not hesitate. Show no mercy. . . . Once more, the Sith will rule the galaxy, and we shall have peace.”  By the time of A New Hope, Obi-Wan reveals that Darth Vader “helped the Empire hunt down and destroy the Jedi Knights. . . . Now the Jedi are all but extinct.”  Kylo Ren might have also been taught that in order to insure peace and order in the galaxy, the Jedi must be exterminated.
Why would Anakin embrace Palpatine’s declaration that the Jedi must be destroyed so readily? Anakin’s transition between being a Jedi and taking a lightsaber to young Jedi as a Sith Lord is not handled very well in the movies. It’s too sudden and the reasons (mostly a grudge for not getting a promotion and the desire to save his secret wife) don’t seem sensible or compelling enough to move Anakin to do what he did so quickly. Yet, from the Clone Wars TV series, we get a better glimpse of a gradual transition that happens over the course of the war. Most often, we see validation of his discussion with Yoda in The Phantom Menace when fear for the people he loves consistently turns him to overly-aggressive actions, including using his infamous force-choke in one memorable interrogation session. He also becomes increasingly disillusioned with the Jedi Order because of his relationship with Padmé and a few shady things that he found out the Jedi order was doing during the Clone Wars that led him to feel a bit betrayed. This included faking the death of Obi-Wan Kenobi for a mission and ejecting his padawan from the Jedi order when she was framed for a crime when she was innocent. When Ahsoka decides to remain outside of the Jedi Order after her innocence was proven, Anakin confides in her that: “I understand. More than you realize, I understand wanting to walk away from the Order.” 
We also see public opinion turning against the Jedi in ways that may mirror Anakin’s inward opinion of the order. In a Godzilla-inspired episode we see an advertisement playing in the background with Palpatine dismissing a “rumor of the Jedi prolonging the war to give themselves more power.”  Later, a citizen of Coruscant stated that: “There are some citizens of the Republic, like myself, who believe the Jedi order is not what it used to be. The Jedi have become warmongers. They’ve become military weapons and they’re killing when they should be keeping the peace.”  At that time, a Jedi by the name of Barriss Offee had bombed the Jedi Temple on Coruscant. When captured, Offee also explained that:
I did it because I have come to realize what many people in the Republic have come to realize: That the Jedi are the ones responsible for this war. That we’ve so lost our way that we have become villains in this conflict. That we are the ones who should be put on trial, all of us! And my attack on the temple was an attack on what the Jedi have become—an army fighting for the dark side, fallen from the light that we once held so dear. 
Anakin came to believe that Barriss was speaking the truth. In Revenge of the Sith Mace Windu states that they need to remove the Chancellor and that “the Jedi Council would have to take control of the Senate in order to secure a peaceful transition.” After apprehending the Chancellor, Windu proclaims that Palpatine is “too dangerous to be kept alive” and must be killed without a trial.  This comes across as a final confirmation to Anakin that his fears are true. The Jedi have fallen and are using the war to seek power. Thus, Palpatine’s command was accepted because Anakin had come to truly believe that the Jedi were villains. Following the Clone Wars and Order 66, Darth Vader spearheaded the efforts to eliminate any remaining Jedi. He oversaw the training of dark side users assigned to hunt and destroy Jedi and his castle on Mustafar become known as the place where Jedi go to die.  He was successful enough that Yoda told Luke in Return of the Jedi: “When gone am I the last of the Jedi will you be.” 
This task—to eliminate the Jedi—may be the great task that Kylo Ren felt he needed to finish for Darth Vader. He was known as the “Jedi killer” and was responsible for exterminating the Jedi Temple that Luke established in the years following Return of the Jedi. In The Force Awakens, he was determined to find Luke Skywalker, even nearly disobeying Supreme Leader Snoke’s orders to ensure that he could have the map. Snoke feared the Jedi and did not want Luke’s return, but seemed more than willing to let him live out his days in obscurity, while Kylo Ren was determined to seek him out, whatever the cost. As the last Jedi, Luke would be the final thing that stood in Kylo Ren’s way of accomplishing a goal of completely exterminating the Jedi order. Perhaps this quest came in part because he idolized Vader, but also perhaps partly because some shocking information he discovered about the Jedi order while exploring their history with Luke.
The current trend in Star Wars literature does indicate that the Jedi order was severely flawed, which is what caused their downfall. In the Ahsoka book released last year, it is stated that Ahsoka (Anakin’s former apprentice) felt that Barriss’s opinion was accurate, even if her actions were evil. Pablo Hidalgo—the current “King of Cannon” in the Star Wars Universe (and a member of the team that determines where Star Wars is going) tweeted about the nature of the Force. He noted that using midi-chlorian counts as a prerequisite to enter the Jedi Order in the Prequels was “a rather soulless way to look at potential, by narrative design. The prequel Jedi have systemized their methods at the expense of spirituality and intuition. They are more ‘Order’ than ‘Jedi.’”  The legalism that individuals like Qui-Gon Jinn and Anakin bucked against was an issue plaguing the order, in addition to jumping into the Clone Wars. Further problems with the Jedi Order are mentioned in Attack of the Clones, where Jedi masters talk about increasing frequency of personality flaws like arrogance among the Jedi and diminished ability to use the Force.
There is also the issue of balance in the Force. In the Last Jedi trailer, Luke is heard talking with Rey:
Luke: “Breathe. Just breath. Now reach out. What do you see?”
Rey: “Light. Darkness. The balance.”
Luke: “It’s so much bigger.”
This indicates that finding balance in the Force might be a focus for Luke. In Episode 1, Qui-Gon believes that Anakin is “the Chosen One,” an individual destined to fulfil a prophesy and “bring balance to the Force.”  Throughout the Prequels, Anakin is portrayed as the Chosen One, climaxing with Obi-Wan’s anguished exclamation after Anakin turns to the dark side that: “You were the Chosen One! It was said that you would destroy the Sith, not join them. It was you who would bring balance to the Force, not leave it in Darkness.” 
This statement by Obi-Wan has caused some debate about whether Anakin or Luke were the Chosen One. George Lucas confirmed in an interview on the Revenge of the Sith DVD release that Anakin was still the Chosen One. He said:
I think when you watch the movies in order, the story will become very clear, that Anakin is the Chosen One. And even when Anakin turns into Darth Vader, he is still the Chosen One. . . . The Prophesy states that he will bring balance to the Force and destroy the Sith. He becomes Darth Vader. Darth Vader does become the hero. Darth Vader does destroy the Sith, meaning himself and the Emperor. He does it because he is redeemed by his son. So the Prophesy is true. And by doing that, he redeems himself and goes from being Darth Vader back to being Anakin again. 
Thus, Anakin did fulfil the prophesy as the Jedi believed in it.
Things may be taken a different way, however, now that Lucas is no longer in charge. Recently, in the Star Wars Rebels series, Obi-Wan told Maul that Luke was the Chosen One.  This may just be Obi-Wan’s point of view at the time, but it might be a route that is taken by the Star Wars group—that Luke is the Chosen One and still needs to bring balance to the Force in some way beyond exterminating the Sith. Perhaps this plays into the flaws of the Jedi order during the Prequel Era—that Luke needs to correct some teachings to make it more balanced. In the novelization of The Force Awakens, an in-universe text known as the Journal of the Whills contains a statement that “First comes the day/Then comes the night./After the darkness/Shines through the light./ The difference, they say,/Is only made right/By resolving of gray/Through refined Jedi sight.”  This points towards Luke making things right in the universe by resolving the grey areas of the Force and bringing some sort of balance though a new order. This is part of why Luke sought out an ancient Jedi temple—to learn what the Jedi Order was like at its beginning before it became a shell of what it was meant to be.
This Chosen One mythology may also be part of how Snoke seduced Ben to the dark side. The Visual Dictionary for The Force Awakens states that Snoke is interested in Kylo for his mixture of light and dark. As it states in the text itself: “Having studied Jedi skill as well as arcane dark side lore, Kylo Ren is the embodiment of conflict, drawing upon contradictory teachings and deriving power from discord.”  And also: “The Supreme Leader believes Ren to be the ideal embodiment of the Force, a focal point of both light and dark side ability.”  Although Snoke is, in the words of J. J. Abrams, “a powerful figure on the Dark Side of the Force,”  and Kylo Ren seeks immunity to the light side, Kylo Ren may have convinced by Snoke that he is the Chosen One, fulfilling his grandfather’s destiny. This is speculative, but a possibility.
The issue of balance in the Force also hinges on what the creative team at Lucasfilms considers the nature of the Force to be. One interpretation is that the Force is a benevolent power with a will of its own, and the dark side is a corruption or misuse of that power against its own will—a cancer that must be cut out. Thus, balance is achieved when the dark side is not being used. The other interpretation is that the Force either has two sides or there are two separate Forces constantly at war with each other—the light and the darkness. Balance is achieved when both are held in equilibrium. Anakin could still be the Chosen One either way—purging the galaxy of the Sith that pushed it off balance in favor of darkness and allowing the universe to regain its center of balance or cutting out cancer and allowing the light side to become dominant again. Luke could also be the Chosen One if the latter is true.
George Lucas has made a few statements in support of both theories over the years, though there is a lot of evidence that points to the latter theory. For example, he said that: “The Force has two sides. It is not a malevolent or a benevolent thing. It has a bad side to it, involving hate and fear, and it has a good side, involving love, charity, fairness and hope.”  Later, he added that: “In each of us we to have balance these emotions, and in the Star Wars saga the most important point is balance, balance between everything.”  “I wanted to have this mythological footing because I was basing the films on the idea that the Force has two sides, the good side, the evil side, and they both need to be there. Most religions are built on that, whether it’s called yin and yang, God and the devil—everything is built on the push-pull tension created by two sides of the equation. Right from the very beginning, that was the key issue in ‘Star Wars.'”  These indicate that the Force is one entity with two aspects that must be kept in balance.
Even in-universe references support a balance through walking a middle road between light and darkness. During the Clone Wars TV series, it is stated by a being with deep understanding of the Force that: “The light and the dark. Day with night. Destruction, replaced by creation…. Too much light or dark would be the undoing of life as you understand it.”  We have also seen characters like Ahsoka and the Bendu who have embraced a “balanced” middle-road approach between the light and dark during the Star Wars Rebels series.
The terms used by the Bendu character for the light and dark are Ashla and Bogan, terms rooted in George Lucas’s early concepts in designing the Force. These terms were used in a Legends (old stories not included in the current cannon) comic book that discussed the earliest proto-Jedi Order. According to the text, the group believed that they should “be a prisoner of neither Bogan nor Ashla. Strive to live in balance.”  Although not a part of the Star Wars Cinematic Universe, Legends stories are known to the creative team at the helm of Star Wars and may inform the direction they take. If the Bendu is any indication, there is a distinct chance that this Ashla-Bogan lore is being incorporated into the current universe. There is no solid evidence yet that the earliest Jedi order believed in this sort of balance, but if Luke is seeking out the earliest Jedi temples to learn what they believed and is rambling about balance between light and darkness being so much greater (as he is in the trailer), that may be the direction they’re going.
The trailer for The Last Jedi brings up more questions than answers (as it should), and hopefully we’ll see them addressed in the movie this December. It’s possible that Luke will bring balance to the Force as he works through his own faith crisis. Perhaps both he and Kylo Ren have taken the courses that they have because of some shocking revelation they found during their research together into the Jedi Order. In Kylo Ren’s case, this sent him spiraling off into the dark side, seeking to exterminate all Jedi and rule the galaxy. In Luke’s case, it sent him into exile, fatalistically believing that Jedi should no longer walk the galaxy. Whether this is true or not, and what will come of it remains to be seen.
 Star Wars Episode VII: The Force Awakens
 Star Wars Episode VII
 Star Wars Episode II: Attack of the Clones
 Star Wars Episode III: Revenge of the Sith
 Star Wars Episode V: The Empire Strikes Back
 Star Wars Episode III
 Star Wars Episode III
 Star Wars Episode IV: A New Hope
 Star Wars, the Clone Wars, Season 5, Episode 20
 Star Wars, The Clone Wars, Season 2 Episode 19
 Star Wars, The Clone Wars, Season 5, Episode 18
 Star Wars, The Clone Wars, Season 5, Episode 20
 Star Wars Episode III
 See Star Wars Rebels, Seasons 1-2
 Star Wars Episode VI, Return of the Jedi
 Star Wars Episode I, The Phantom Menace
 Star Wars Episode III
 Star Wars Rebels, Season 3, Episode 20
 Alan Dean Foster, Star Wars: The Force Awakens (New York: Del Rey, 2016)
 Times Magazine, 1980, cited http://www.swtor.com/community/showthread.php?p=7201993
 Time Magazine, 2002, cited http://www.swtor.com/community/showthread.php?p=7201993
 Time Magazine, 2002, cited http://www.swtor.com/community/showthread.php?p=7201993
 Star Wars, The Clone Wars, Season 3, Episode 15.
 Star Wars: Dawn of the Jedi: Force Storm 1, cited at http://www.swtor.com/community/showthread.php?p=7201993