I just re-read one of the Delsarte acting posts I put up months ago. Gee, I didn't do a very good job of explaining it. Let me try again, using my own words and my own sketches this time.
Delsarte believed that certain movements are highly symbolic and powerful. When you're happy you want to throw your arms up in the air. When you're sad you want to put your head down and slump forward. Probably everybody in the world recognizes and uses these gestures...everybody except actors.
Delsarte believed that actors avoid these obvious gestures because they seem too over-the-top, too caricatured. He thought that was a pity because no other gestures convey so much power. He created a system for using gestures like these without looking ridiculous.
In the sketches above, drawing A is a watered down version of the gesture that's full strength in drawing B. The second has a lot more power, especially when seen from the side, but it might be too strong for some scenes. Delsarte says, use the broad gesture anyway, but do it at an angle that would flatten it a bit from the audience's point of view, as in drawing C. Interesting, huh?
Delsarte wanted to bring broad gestures like the one on the left above, back to acting. Of course extended arm poses aren't the only type of broad action he was interested in. The guy on the right doesn't simply talk to his friend to get his attention, he grabs his arm before speaking. That conveys to the audience that what the speaker's saying is important. The arm grab's a powerful symbol and Delsarte wonders why we don't use it.
Sometimes a gesture combines two powerful symbols. Here's (above) a gesture indicating strong emotion that ends with a strong but unexpected "come hither" gesture.