William Wordsworth was a Romantic poet, and Romantic poets often celebrated the natural world for its beauty and grandeur. At the beginning of the poem, the speaker indicates that before he encountered the beauty "of golden daffodils," he felt as "lonely as a cloud." However, as soon as he saw the daffodils, "fluttering and dancing in the breeze," he says that he "could not but be gay / In such a jocund company." In other words, seeing the beauty of the daffodils, the speaker could not help but be happy, because the daffodils provided him with such joyful company. The implication here is that the beauty of the daffodils, from the perspective of the speaker, is synonymous with their ability to make him feel joyful and no longer lonely.
The speaker also suggests that the daffodils are beautiful because they inspire him. In the final stanza of the poem, the speaker says that often when he is in "vacant or in pensive mood," he recalls the beauty of the daffodils. The daffodils, he says, "flash upon that inward eye / Which is the bliss of solitude." The implication here is that when he recalls the beauty of the daffodils, the speaker feels an awakening of "that inward eye" which is the seat of inspiration for the poet. This idea is suggested also in the penultimate stanza of the poem, when the speaker says that, seeing the daffodils, "a poet could not but be gay." The fact that the speaker says that the beauty of the daffodils must appeal specifically to "a poet" suggests that their beauty derives from their ability to awaken one's poetic inspiration.