Why is the sky lower than the trees in the poem "how wide the world was, how close the trees to heaven, and how clear in the water the nearness of the moon!"?

it is easy to understand. When you look up at the sky, it is of course high. But when you look at the distance, especially when the sky meets the earth, it is of course very low. When the poet looks at a relatively close tree, he sees the sky just above the horizon, so the sky is lower than the tree.

it's easy to understand being close to people. Qing Jiang, the moon must have a reflection in the water. The poet is in the boat again, and of course he will feel close to the moon.