This is a farewell poem. The main idea of ??the poem is: after the stream crosses the bridge, it never comes back, and the boat has to rely on short poles to prop it open. Friendship is as long-lasting as the crossing of mountains and rivers. It will always be there no matter the wind or waves.
One or two sentences describe the scenery, creating an atmosphere of saying goodbye to friends. Three or four sentences speak directly from the heart, expressing the theme that friendship is everlasting and can withstand the test of wind and waves.
This poem mainly uses contrasting techniques, using "the stream will never return to the bridge" and "no matter the storm comes and goes" to highlight the permanence of friendship. In addition, the use of metaphors directly compares "friendship" to "crossing mountains and streams", and uses "turbulence" in nature to symbolize social disturbances, thus highlighting the theme of the poem.