The narrator with a melancholy and remorseful admission that he knows exactly what it must be feel like to be a bird kept in a cage. He then gives life this admission by contrasting the visceral everyday experiences of nature that a bird not trapped inside such a prison enjoys: bright sun, soft winds and the waters of a river. He brings the parallel to a close by describing how the normally enjoyable sounds of the first bird whistling in the morning and the first flower bud opening to let loose its sweet scent are to one trapped inside not so much enjoyable, but a part of the experience of losing freedom.
He then goes on to reveal how much is aware of the experience of being trapped like a bird by explaining the actions that such birds often demonstrate. Birds in captivity flutter their wings violently as a reaction to unwanted but repetitive requirement to use those wings to fly to the only place he can possibly fly to: his tiny little perch. The pain caused by every one of those violent fluttering of its wings can be felt each time he longs to stretch those wings out in the open, but is only allowed to sit in the same space doing the same thing day after day after day.
The poem concludes with the narrator one again regretfully admitting he knows why the bird in a case continues to sing even when its wing is sore from the fluttering and its heart is heavy from longing for a freedom that will never come. The song that the caged bird sings does not originate in happiness; indeed, it is not even really a song he sings. It is a prayer and plea masquerading as a song; a plea and prayer sent straight from its wounded heart upward and outward in search of some greater power capable of releasing it from its prison and relieving it of its misery.