Wordsworth's poems teach us that observing and appreciating nature can bring us closer to God and give us joy. Through interacting with nature, we can also build up a store of memories that sustain us through sadder times.
The line "Let nature be your teacher" comes from Wordsworth's poem "The Tables Turned," in which the speaker tells a friend to leave his studying behind because he can learn more from a walk in the woodlands and the song of the birds than from his books. The speaker tells his friend that nature will teach him more:
Of moral evil and of good,
Than all the sages can.
Wordsworth repeats this theme of nature as a guide through many of his poems. In "Lines Composed a Few Miles above Tintern Abbey," he writes of the joy nature brings him, saying that in it he feels the awe of God's presence:
A presence that disturbs me with the joy
Of elevated thoughts; a sense sublime.
In this poem and others, he also expresses how nature brings back fond memories. Returning to the Wye and Tintern Abbey periodically, he can recall the happiness of old times and measure his changes.
In his poem "I Wandered Lonely as a Cloud
," he celebrates the joy he feels when he sees a vast field of daffodils bending in the breeze as if they are dancing. Not only does the scene elate him the first time but, lying in his study in winter, he can repeatedly recreate the joy he felt through memory. Likewise, he can derive repeated joy from the memory of the song of a solitary young woman singing in the Scottish Highlands.
Wordsworth understood himself as a poet sage in the mold of Milton, explaining the ways of God to man (humankind). But rather than writing a grand epic poem on Biblical themes as Milton did, he wrote lyric poems that celebrate the simple but sublime joys of nature that are available to everyone.