While Lego pieces are nominally for building whatever your imagination can come up with, we all know what the licensed ones are for: Building the picture on the box.
And as Lego's ever-increasing suite of licensed properties shows, there's also a desire (either among kids or among toymakers) to put your set together and act out one of the notable action sequences or plot beats of the movie. In this case, the ad encourages kids to "build the X-wing and save the droid."
Now, that could just be a riff on a common phrase like "save the girl." Or, like the Lego set that revealed Pepper Potts in the Iron Man suit before Iron Man 3 ever hit theaters, it could be a hint at how Poe Dameron, Rey and Finn all wind up in the same place.
Not to mention the possibility that, just like A New Hope, The Force Awakens may concern the adventures of a little droid who is much more important than he looks.