Observation is developed by singleness of glance. For instance, if I look at a person, I can see that one person much better than if I looked at many persons. It is like this with everything in life. The first step in learning mysticism is just this to develop our observation. We are always looking at a hundred thousand things around us, and never study one properly at all. To understand and know a thing better you keep looking at it. If you keep looking at everything, you look at nothing! Such is the "law of observation."