Just reading the title the reader may aspect the poem is sitting in the country just because the reaper work in the fields.One interesting elemen may draw the attention is the use of the choice may anticipate  a melancholic atmosphere or a sad one.The speaking voice invite the porser-by to invite to look who is singing and reaping.the sound is melanholic and the sing fill all the valley whit an echo effect.She is singing a gloomy song, but it fascinates the author so much that he even considers it sweeter than the one of a Nightingale and compares the girl's voice to the one of the Cuckoo- birds, which break the silence of the seas. But, since the poet doesn't know the dialect of the song, he cannot comprehend its meaning. Anyhow, he speculates that it may be about an unhappy memory, some battles fought long before, or about the common pain of everyday life. The song has such a great impression on the poet, that even when he mounts up the hill and cannot hear anymore the girl's song, he still keeps it in his heart.The poem is made up of four eight-line stanzas, written in iambic tetrameter. Each stanza follows the rhyme scheme of ABABCCDD, but in the first and the last stanza, the "A" rhyme is off.
The language used by the poet is simple, since there isn't any artificial or poetic diction: it is natural and unforced. The author uses the "simile" in the second stanza, where he compares the girl's song to the one of a nightingale, and her voice to the one of the Cuckoo-birds.
The poem's structure is simple: in the first stanza, the author introduces us the rustic landscape in which the poem is set, as well as the highland lass, who's the protagonist; in the second he flatters the girl's song, by comparing it to the one of Nightingale and the Cuckoo-birds; in the third he wonders about the content of the song; and in the fourth he describes its effect on himself. The choice of a completely natural landscape as the setting of the poem makes us understand the importance nature had for the poet, He considered it as man's source of inspiration and as the only way for him to come in contact with moral and spiritual values. Anyhow the poem is about the girl's song. Even though the author cannot understand it because he doesn't know its dialect, he appreciates its tone, its musicality and the mood that it creates inside himself. So, the poem ponders the limitation of language, but the author really wanted to praise the beauty of music. Additionally, the last two lines of the poem focus on the theme ,already used in "I wondered lonely as a cloud", of memory and the beautiful effects they have on men.