What is written in The Yellow Crane Tower's Farewell to Meng Haoran on the Way to Yangzhou? What is the central meaning?

The old friend said goodbye to me at the West Yellow Crane Tower and went to Yangzhou in the misty and flowery spring of March. The sail shadow of the lonely boat drifted away and disappeared at the end of the blue sky, only to see the Yangtze River flowing to the horizon.

Li Bai's contact with Meng Haoran was just after he left Sichuan. At that time, he was young and happy, and the world in his eyes was almost as beautiful as gold. Meng Haoran, more than ten years older than Li Bai, has become famous for his poems. The poet sent his friend on a long trip, and he was full of envy for his old friend going to the bustling Yangzhou. His poems were filled with cheerful emotions.

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The poet's overlook on the river shows the deep friendship between them.