How we cite our quotes: (Line)
Quote #1
Alone she cuts and binds the grain,
And sings a melancholy strain; (5-6)
The woman's song is very close to nature. The rhyme on "strain" and "grain" tells us that for sure. "Grain" (a plant) goes with "strain" (a song). Lots of poets have said that art and nature are opposed to one another, but here they are totally vibing.
Quote #2
O listen! for the Vale profound
Is overflowing with the sound. (7-8)
The "Vale" can't get enough of the woman's song. It is literally overflowing with the sound of it, as if the natural world were also an ecstatic spectator.
Quote #3
No Nightingale did ever chaunt
More welcome notes to weary bands
Of travellers in some shady haunt,
Among Arabian sands: (9-12)
The natural world is full of singers, like the nightingale described here. While the reaper is very close to nature (she lives and works in the fields), she's not quite a part of it. Her song is way different from the bird's song.
Quote #4
A voice so thrilling ne'er was heard
In spring-time from the Cuckoo-bird,
Breaking the silence of the seas
Among the farthest Hebrides. (13-16)
As in lines 9-12, despite the solitary reaper's special relationship to nature, she's still not quite one with it. Her song is different than the cuckoo-bird's song, way out there near the Hebrides. The implication is that you could travel "way out there" (to the Hebrides) and still not find a natural counterpart.