What Is the Deal With Chapel Perilous?

There are two main deals in Crowley's system. He calls the knowledge and conversation of the Holy Guardian angel. The second one he calls crossing the abyss is supposed to be the sort of separation between the world of illusion and the real world. When you go into chapel perilous there can be a point where all those, Grirjev calls them buffers, all those things that separate you from everything else kind of collapse.