He is directing his attention to his friend, St. John (prounounced "Sin-jin"). Because he refers to him by his given name and not by his title, you can tell that the author is friends with St. John.
ex·pa·ti·ate ( k-sp sh - t ). intr.v. ex·pa·ti·at·ed, ex·pa·ti·at·ing, ex·pa·ti·ates. 1. To speak or write at length. In other words--Pope is inviting his friend to a read/write a long, probably philisophical analysis, of "this scene of man." Humanity?
He gives his first choice here, building upon the maze idea . . . do you take one path or the other? One explanation or the other? Is life a place of weeds or a garden? Do we have "promiscuous flow'rs" or "forbidden fruit"?
"Beat" the field can refer to both beating a field to scare game out of it, and beating wheat or barley to remove the seads for harvesting. He is asking his friend to look deeply, to scare the hidden things out of the "field of man."
Interesting, in this choice we are either blindly creeping or blindly soaring. In other words--whether we are moving quickly or slowly, whether we are in the dirt or in the sky, we are all blind to what is here. This is a further development to the idea of the maze.
Eye Nature's walks, shoot folly as it flies,
14And catch the manners living as they rise;
A development of the idea of the harvest or the hunt and beating the unseen out of the scene. Shoot "folly" (stupidity) when it flies up like a frightened game-bird, or catching manners. He is "personifying" these characteristics.
This is an example of how to annotate a literary piece. Everyone will will have something different to say. There is no right or wrong. These are like discussions with yourself.
This is a list of literary terms for introductory literature courses. It is helpful because it is simple and straight forward, and doesn't get bogged down with too much detail.
Here is a wiki that expresses the motivation behind Rousseau's first and most famous work. It gives great feedback as to what people thought of his ideas.
Cool youtube clip of The Garden of Forking Paths being acted out. Theres a little comedy involved but the overall theme as it relates to the story is the same. Enjoy