The important idea in the story is the value of freedom. No one should be denied his  freedom. Absence of freedom suffocates a person, and prevents him from enjoying the beauty of life in its fullness. The bird in the story was happy flying. It sang beautifully and ate well. However, when it was caged , it became sad, and didn't eat or sing, it required its freedom and if it couldn't sing it would die. This indicates that the beauty of life is in freedom, and not in captivity. 
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