The speaker in this poem is the poet, recalling a "lonely" walk he once took. As he walked, he came upon a "never-ending line along the margin of a bay;" a large expanse of daffodils blowing in the wind.
Watching the flowers "fluttering and dancing in the breeze," Wordsworth compares them to the multitude of stars in the night sky. He observes the water in the lake being blown into waves, but finds that the daffodils "out-did the sparkling waves in glee." In the presence of the cheery color and joyous motion of the daffodils, Wordsworth finds his own mood lifted from the loneliness of his solitary walk to joy in the beauty of the sight.
The true value of the experience, however, doesn't become apparent until later. Wordsworth discovers years later that, "When on my couch I lie In vacant or in pensive mood," the memory of that sight comes back to lift his mood. As he recalls the beauty he beheld, "my heart with pleasure fills, And dances with the daffodils."