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Luke Skywalker was the only character to speak in the trailer. And I want to break down his lines and what I think they mean in this chapter.
These words were spoken by Luke:
"We've passed down all we know.
A thousand generations live in you now.
But this is your fight.
We will always be with you."
I think that basically everyone knew that Luke was going to be in Episode IX, and this confirms it.
To me these words means that Rey already knows all of the Jedi teachings, perhaps Luke finishes her training as a Force ghost and these are the words he speaks to her as she completes her training. He has taught her all he knows. "We've passed down all know."
But... "we've passed down all we know."
We! What if Luke wasn't the only one teaching her. What if Yoda was also training her, or Obi Wan Kenobi, or maybe even Anakin (please!). Or better yet, all of them!
"A thousand generations live in you now."
A thousand generations of knowledge now live in Rey.
"But it is your fight."
Rey must fight Kylo Ren alone. Luke knows that Rey is the only one strong enough to face and fight Kylo Ren. But Luke also knows that she is also the only one strong enough to save him.
"We will always be with you."
This sounds like something he might say just before he and whoever is with him fades away. It could be Yoda, Obi Wan Kenobi, Anakin Skywalker, Leia, (if she dies and becomes a Force ghost) or Ben's Force ghost, which is making me cry. I can't even see what I'm typing right now.
I am imagining Ben dying as he is redeemed, and becomes a Force ghost. Then Luke says this line to Rey and Ben smiles at her, and then they both fade away.
I am still crying.
Sorry, back on topic.
The last line spoken by Luke in the trailer was his line from the Last Jedi. "No one's ever really gone."
That symbolizes so much for Episode IX, we all know that Luke is coming back, and perhaps others. But most importantly it symbolizes what Luke meant when he said it. Ben isn't gone.
"Leia after so long stirred some embers inside her.
"This is the end... isn't it?" She asked.
Luke's eyes had a strange glint. "I came to face him, Leia. And I can't save him."
"I held onto hope for so long." Leia shook her head. "My son is gone."
The glint in Luke's eyes got even stranger. "No one's ever really gone." He said.
That was the old Luke talking, the Luke she'd once known who could discern even the dimmest light in the darkest of hearts. He had found a way to redeem a man she never could- their father. If Luke couldn't save Ben, maybe he believed someone else could.
Leia placed her hand on top of his and her weariness faded away. When Luke withdrew his hand she held in hers a pair of chance cubes- Han's dice, which he'd hung in the cockpit of the Millennium Falcon. Luke must have taken it from the Falcon, meaning he must have met Rey. Might he have taught her something? Could the girl from Jakku somehow help them all, even Ben?
Leia smiled. Maybe the Resistance and the galaxy still had a chance."
This quote from the Novelization confirms that he was talking about Ben when he said it. Ben Solo will be redeemed in Episode IX.