Can be subtle, not necessarily explicit. The theme should be included in the specific narrative and description, and it is generally not appropriate to reveal it with obvious words. For example, the industrious quality of characters should be expressed through concrete things and vivid details, and it is not appropriate to label characters with the word "industrious".
Another example is to describe a meaningful thing. It is not appropriate to talk about its "meaning" in an empty and abstract way, but to show it naturally in a specific plot. Engels said that the more hidden the meaning of the event and the character, the stronger the artistic charm of the work.
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"On the Autumn Night" depicts a scene by the river in autumn dusk. From the overall framework, this poem adopts the popular style of short poems, short descriptions, concise outlines, prose sentences and improvisation, all of which show the style of Tagore and Japanese haiku.
In the 1920s, poets who wrote new poems were greatly influenced by old poems, so all the new poems at that time had a strong style of old poems. In addition to writing in vernacular, the artistic conception and expression of poetry are often not much different from those of old poems. This is a major feature of poetry at that time.
The same is true of Liu Dabai, the author of this poem. Although he tried to write a pure vernacular poem, the rhyme of this poem still follows the original requirements of classical poetry, so we can still see the traces of its influence by old poems. "Autumn Night on the River" was created in this environment.
"The bird that returned to its nest, though tired, still came back with the sunset." The tired bird wanted to go back to its nest. At that time, it was getting late. The afterglow of the sunset shines on the bird's back and wings, as if bringing the sunset back to its nest. The evening scenery, in the poet's pen, has a sad beauty.