"Caged Bird" 3rd stanza:
The caged bird sings
with a fearful trill
of thing unknown
but longed for still
and his tune is heard
on the distant hill
for the caged bird
sings of freedom
My paraphrasing of this stanza: the caged bird is afraid of the things he does not know because he is trapped, but he would like to know them because that would mean that he would be free to go. He can only use his voice, and sings of freedom and things that not everyone likes to hear. But since his voice is all he has, he sings demanding freedom and his voice cannot be caged, so it reaches everywhere.