The popular use of the word "immediacy" implies a direct and instant involvement with something. The word implies closeness and inclusion. In literature, immediacy refers to the condition of feeling so close to a certain experience that the medium disappears. For example, a painting looks so realistic that the person forgets he is looking at a painting, and not at the real object.
This passage could be considered an example of immediacy due to its vivid description. The image is so real and so mundane a person could imagine himself actually present at the scene, as opposed to simply reading about it.