There are a few things William can tell just by the way that Gabriel is acting, from the things that he's saying. The first one is glaringly obvious; that his other self isn't anyone of any kind of importance. Had it been so, the Archangel would have said it by now instead of circling like a cat stalking it's prey. Which meant the obvious disrespect. In a way it was interesting to see this one talking and acting like he was in charge of the whole thing, William just turning his head slightly to follow Gabriel's path. Sure, there's a knife in his other hand behind his back, but that's just in case.

"No point in attacking you, that would benefit no-one at the end of it all. I'm only armed in case you feel the need to do something stupid. Anyway, you've not said anything original to warrant my full attention since you got here. Considering I hear God, you have your work cut out for you."