The point of all this is to have a practice that involves only ourselves, our image in the mirror, and the voice coming down to us from the ceiling. (There are times in class when I lose track of where the teacher is. The dialogue always comes from the same direction, so it's perfectly possible to come out of a pose having totally lost track of where the teacher is in the room.) Focusing only on ourselves, when things are going well, its possible to shut out the outside world, and become completely involved in the poses.
I think that's what Gates means by cultivating emptiness. And I love his conclusion about this process of letting go of everything but awareness of the present: "Into this emptiness, grace will come."