The first couplet of Zhao Mengfu's Poems on the Reading of Ancient Poems describes what kind of scene and what role it plays. Please analyze it briefly.

Original poem:

The east wind blows willow flowers in the stream, and there is no sand in the spring water at the head of the stream.

Bai Ou is confident in his own affairs, but this mysterious bird still knows that he is old.

This is not yesterday's dream. Whose is Shengfeng Dragon Tube?

It's painful to think of Dongling, and I want to ask about planting melons in gardening.

The east wind blows willow flowers on the stream, and the spring water at the head of the stream is as clear as sand. Bai Ou's confidence has nothing to do with it, but Blackbird knows that time is limited. Is it yesterday's dream that colorful Hu boats pull ivory masts? Whose beard is Shengfeng Dragon Tube? All this makes people miss Donglingzi's difficulty and return to pastoral studies to grow melons.

The east wind blows the willow flowers on the stream, and the spring water at the head of the stream is as clean as if there is no sand. The scenery on the stream depicted by line drawing reflects the poet's praise of the scenery and his carefree mood.