The nightingale [... / ...]
Sings out her woes, a thorn her song-book making
The main noun/verb pair of the sentence that makes up the first eight lines is spread across lines 1 and 4. However, looking at them together, we can see the main subject of the poem: the nightingale’s song, and in particular, the way that song enables her to turn her pain into art. This is a central theme of the poem. It is even more significant because the speaker states that he does not have the same capacity—although this claim is debatable.
O Philomela fair, O take some gladness,
That here is juster cause of plaintful sadness:
Thine earth now springs, mine fadeth;
Thy thorn without, my thorn my heart invadeth.
This refrain makes up the final four lines of both stanzas one and two. It is important because it reveals the main symbol of the poem: the nightingale is not just a bird, but Philomela. In directly addressing Philomela with these lines, the poet twice tells her that she should “take gladness” in the fact that the speaker’s pain has a “juster” cause of sadness than she does. If she looks at his inability to express himself, she should feel glad that she, at least, can sing out her pain.
As this refrain is repeated twice, however, it develops has a second interpretation. In becoming the refrain or chorus for a poem set to song, it shows that the speaker—just like Philomela—actually is able to turn his pain into art. This challenges his credibility, and especially his minimization of Philomela's rape.
