Answer:
When he beats his bars and he would be free;
It is not a carol of joy or glee,
This is the first time that the speaker tells us explicitly why the caged bird is singing: it wants to be "free." This sets up freedom as an important idea in the poem. This is a poem about a bird wanting, but not being able, to get free.
These lines continue the alliteration of the B words, in "beats" and "bars." B is a strong sound, and the repetition of this sound evokes the idea of the bird beating violently against the bars of its cage.
So, when we hear that really pretty song the bird sings in its cage, we shouldn't assume that it's singing because it's happy. As the speaker tells us, "It is not a carol of joy or glee."
Does this help?
