The speaker is a writer wrestling with his own creative life. He calls his pen "my lady" and wonders whether he is really meant to "father a child" with her, which suggests he is asking if he can truly bring something new into the world through writing. His mind is crowded and anxious, full of "pictures pictures pictures" that pile up without settling into anything clear. He feels sick of the "river of gray business," which seems to mean the dull, endless flow of ordinary tasks and obligations.
So he steps outside at night and speaks to her "in her cage." The image is a little ambiguous: the pen, or the creative impulse, seems to be imagined as a captive bird. His words to her are tender and almost apologetic, telling her she was once a "bird of paradise." The mood is quiet, weary, and affectionate, with a note of guilt, as if he fears he has hemmed in something beautiful.