This excellent poem by William Wordsworth is not to be confused with the poem by Shelley with exactly the same title. However, interestingly, both poems are rather similar with their focus on the skylark as a creature who, through its song, is able to transcend the troubles of life.
In Wordsworth's poem, the speaker is walking through "wilderness dreary" and feeling weighed down by the worries of the world. He is attracted to the joy of the skylark's song, and desires to fly up into the sky to be with the skylark in its realm, recognising that there is both a "madness" to the skylark and a "joy divine" in its song. The speaker finds inspiration in the skylark's song, which is "As full of gladness and as free of heaven," to "plod on" in his journey as he has hope for "higher raptures" when he reaches the end of his life.