The lines suggest a feeling of calm, of being transfixed by the light dropping through the tree branches. The poet creates this feeling first with the setting, “Under the trees.” Then, the phrase “a green/latticework of branches” compares the broken pattern of light to the crossed patterns of tree branches. This suggests a peaceful setting. He finishes the stanza with the image of the light as“drifting down like clean/white sand.
The /s/ sounds in “cicada sends/ its sawing song” suggest the repetitious, raspy noise of a cicada itself.
Yes, the poem expresses an appreciation for how light enhances the beauty of sights and sounds in nature.