Why did he feel that she is unhappy?
The speaker of the poem, who is presumably Wordsworth himself, assumes that this solitary Highland Lass is unhappy because of the song she is singing. The melancholy song seems strikingly appropriate to the setting, in which there would be complete silence except for the girl's song. In the first stanza he says:
Alone she cuts and binds the grain,
And sings a melancholy strain;
Perhaps the plaintive numbers flowFor old, unhappy, far-off things,And battles long ago:Or is it some more humble lay,Familiar matter of to-day?Some natural sorrow, loss, or pain,That has been, and may be again?
As if her song could have no ending.
Poetry is the spontaneous overflow of powerful feelings: it takes its origin from emotion recollected in tranquility.
The music in my heart I bore,Long after it was heard no more.