The Edit. It allowed the film to travel through time and space. Also allowed for multiple angles/shots within a single scene, from which was also born the idea of doing multiple takes. And finally, its use doesn't just set the pace, but can amplify/modify the tone and feeling of a scene or movie if used properly.

p.s. For those interested, an excellent playlist of Film and Movie Firsts from early cinema can be found here: http://www.youtube.com/playlist?list=PLEBF1422257264B00&feature=plcp