What do spring, cloud, moon, wind, rain and Zhongshan mean?

"Spring is flowing, clouds are flowing, the moon is moving, and the rain is moving in the mountains" is a couplet that describes the moonlight pouring down from a mountain with dense branches and leaves, like a waterfall, smooth as silk, like brocade forging. This sentence can also be used to describe a calligraphy work, which shows the beauty of natural elements such as mountain springs, clouds and moons, wind and rain through calligraphy collection.