How does Gillian Clarke bring out the theme of faith and optimism in the poem "Miracle on St. David's Day"?

In this poem, the symbol of the daffodil, the national flower of Wales and tied inextricably to St. David's Day, serves as a representation of optimism and enduring faith. The daffodil lends its warm color to the "afternoon yellow and open-mouthed with daffodils," and at first, this detail seems as if it could be merely descriptive. However, the frequency with which the daffodils recur in the poem, along with the laboring man's choice of poem—Wordsworth's "The Daffodils"—emphasizes the fact that daffodils, and Welshness, are important and represent a sense of self, individualism, and community which endure in the laboring man although his wits have faded.
As the laborer speaks "hoarse but word-perfect," the daffodils, almost personified, seem to be listening: "still as wax. . . their syllables unspoken, their creams and yellows still." Like a silent audience, the daffodils hear the laborer speak "their syllables" for them. Their presence is so overwhelming, "a thousand, ten thousand," that they seem to have struck a chord in the laborer's mind, helping him remember that "there was a music of speech and that once he had something to say."
The poem's title directs us as to how we should interpret this sudden remembrance from a man who, previously, those in the nursing home believed "had never spoken" in his time there. The emergence of "The Daffodils" from his huge, quiet form, a memory of "a Valleys school," is a miracle of faith and endurance issuing forth, as the daffodils return every spring to symbolize Wales and its patron saint. At the end of the poem, the man's recitation is received with "applause" and with apparent quiet approval by the daffodils, which "are flame," a metaphor which seems to describe them as beacons against the "misery" of men like the laborer.