The day 215 meditation begins with a quote about how eager children are to learn. And when they are learning, they do it with everything -- their whole bodies tend to move. Gates says that asana practice brings us back to this state. Asana involve the whole body.
I think this is one of those things that's easier to see the more you practice. To begin with, for example, the first forward bend might seem like a hamstring stretch. Over time, as you grow into the pose, you start to feel it not only along the hamstrings, but in the lower back as well. Then, you might start paying some more attention into the arms, and the pulling aspect of the pose. One day you hear, and pay attention, to the idea that your head is totally relaxed and your face is on your legs. My face doesn't hit my legs yet, but simply paying attention to the instruction makes a difference. Or you finally hear the bit about getting your arms close together. Over time, it becomes more and more clear that every single part of your body is deeply involved in this one pose. If you wanted, you could focus literally on any part of your body and probably find some room for improvement there.
But Gates point isn't just that. Finally, the goal is to have your attention on everything at once, so that the pose really is a full body experience. At that point, you might take inventory (as Lenette says). But there no longer is a single part of the pose that is the focus. As Gates puts it, the inquiry is ever expanding. It's childlike. Ultimately, if Gates is right, the asana helps us to learn with the openness and the enthusiasm of a child again, with complete attention and no pre-conceptions, using everything we have.