Throughout the trailer it appears that Rey is being trained by Luke. There are glimpses of General Organa, Poe Dameron and BB-8, Finn, Kylo Ren, and Captain Phasma. New starships are introduced.
The two most interesting portions of the trailer deal with balance, what appears to be an ancient text that has the the Jedi symbol on it, and Luke's words at the end of the trailer. He says, "...the Jedi must end." His statement seems incongrus with his actions of training Rey, unless he is teaching her to be in the middle, like Bendu from Star Wars Rebels. Thus his goal may to eliminate the Jedi and Knights of Ren, in order to fulfill the prophecy of the chosen one and truly bring balance to the force.
Star Wars: The Last Jedi stars Mark Hamill, Carrie Fisher, Adam Driver, Daisy Ridley, John Boyega, Oscar Isaac, Lupita Nyong'o, Domhnall Gleeson, Anthony Daniels, Gwendoline Christie, and Andy Serkis. It opens December 15, 2017.