the shadow of the stone pagoda,
the shadow of the pine tree.
I don’t want to get into the habit of “explaining” poetry. Typically we tend to value poetry only for the “point” and cannot appreciate it unless it is understood, but once a poem is “understood” we tend to leave it behind. Rather, we should enjoy the act of reflection.
With this in mind consider the ephemeral “images” given: moonlight, a shadow, a shadow. Consider the difference between a pagoda and a pine tree, consider their similarities…