The speaker/poet continues to bear the song sung by the solitary Scots lass because it sounds so sad and so beautiful. Sad melodies tend to be a bit more haunting than happy ones, and, despite the speaker's inability to understand the maiden, he can tell that it is a "melancholy strain" she sings. Her voice seems to fill up the vale and his soul, and it likely has such a profound effect, in part, because it is so heartrending.

Also, the fact that the speaker cannot understand the maiden's words seems to make the song stick with him longer so that he goes on remembering it even when he can no longer hear it. He asks, "Will no one tell me what she sings?" before he ponders many of the possibilities for the subject matter of the song. Had he known what she was singing about, the song would have lost its mystery and would, perhaps, not have stayed with him because it would not have stirred his imagination the way it does.

In The Solitary Reaper, the poet or speaker bears the song in his heart, 'long after it was heard no more,' because the beauty of the song transcends time. Despite not knowing the theme of the Highland lass' song, the poet tells us that her singing is so beautiful that it exceeds the allure of a nightingale and cuckoo-bird's songs.

In the poem, the poet imagines that the girl may be singing about some old sorrow, or battles of long ago, or mundane dilemma, or perhaps, some private grief which she has experienced and may experience again. The melody and eternal significance of her song appears to speak of universal longings, and the poet finds himself transfixed by her song. Because her song transcends time and space, the poet tells us that he will carry her song in his heart long after it is heard no more.