The poem begins with the speaker asking readers to behold a young girl 'reaping and singing by herself' in a field. The song the girl sings is a sad song, and anyone passing by, the speaker says, should either stop and listen or 'gently pass' so as not to disturb her. He is so struck by the sad beauty of her song that the whole valley seems to overflow with its sound.
In the second stanza, the speaker compares the girl's singing to that of a nightingale and a cuckoo bird. He says that the song she sings is more welcome than a nightingale might sing to weary travellers in the desert, and her voice is more thrilling to hear than the cuckoo-bird in spring. He is utterly enchanted, although, he cannot understand the language of the song and so cannot say what the song is about.
In the third stanza, the speaker tries to imagine what the song might be about. Given its sad tune, he speculates that her song might be about some past sorrow, pain or loss 'of old, unhappy things' or battles fought long ago. Or perhaps, he says, it is a humbler, simpler song about some present sorrow, pain, or loss, a 'matter of to-day.'
