A line from the debut trailer. I'm wondering who is Esbern addressing? Its not the LDB for sure, he speaks of him as if he's not there. And who would possibly be able to stop their return if not the LDB?
http://www.youtube.com/watch?v=B0fQWkk9Z6s

These aren't spoilers cuz the game has been out for year and half now and these details were know even prior to its release.

He's breaking the forth wall and talking to the viewer.

Having interacted with Esbern quite a bit, I feel like that particular line is addressing, in a way, that people ignored him and his life's work.

BUT! There is one they fear... in their tongue he is Dovahkiin... DRAGONBORN! FUS RO DAH

Will never forget that day I screamed like a little kid when this trailer came out. Good times. :'D