Tying It All Together
The entire trailer opens with scenes from the previous 8 movies, starting with the Original Trilogy, through the Prequels, and on to the last 2 films of the Sequels, which emphasizes the point that the Sequels are meant to tie up not just this story but the entire story going back generations, to the days of Anakin the Padawan-turned-Sith lord. The presence of Palpatine certainly confirms this.